The species bank of resupinate Russulales, still in statu nascendi, contains the species with an effused or effused-reflexed basidiome (fruitbody). The species bank sonsists of the following elements: an illustrated introduction to the characters of the group, a morphological character database intended for identification, a sequence database, descriptions and illustrations of the species and a nomenclator. There are also conventional dichotomous keys for checking and for deciding between several species found through the character database, as structure of that database will nor always contain sufficient resolution for identification at the species level.
The coming months the number of descriptions and illustrations will be expanded, and more original sequences will be added.
CBS will be gratefull for additions and corrections, for descriptions and illustrations and positive criticism.
Morphological characters of the resupinate Russulales
I. Macroscopic characters of the basidiome
In the aphyllophoraceous fungi the basidiome displays a tremendous variation in shape. It may be resupinate, effused-reflexed, apodal pileate and spathulate to flabellate or spiculose, pleuropodal pileate with an unilaterally developed pileus and mesopodal, from strictly clavarioid to imbricate-spathulate to infundibuliform or more or less agaricoid. The abhymenial surface is the part of the basidiome that is exposed, bears hymenial structures on the opposite side, but is not covered by these itself and does not belong to the very margin. It is may be glabrous from the start or become so during the development. It may be velutinous, tomentose or strigose and the ‘hairs’ may become organized in squamules or, especially in the basal parts, spiculose structures. The hymenial surface may be smooth, warted, papillate, hydnoid, irpicoid, poroid, irregularly lamellate or provided with ridges. In many resupinate hypochnoid species it is not even completely continuous.
I. Basidiome structure
A basidiome may consist of up to six layers:
a. hymenium, consisting of a pallisade of basidia, with or without additional sterile elements. Sterile hymenial elements may be formed before the production of basidia (catahymenium) or more or less simultaneously (euhymenium); of course they can also be absent. The hymenium may be thickening because of newly formed basidia that replace old ones.
b. subhymenium, from which the basidia arise; when the hymenium is thickening, the subhymenium may become rather thick
c. subiculum, the parallel layer directly on the substratum; it is consequently only present in the resupinate parts.
d. trama, a hyphal layer or hyphal layers between subiculum and subhymenium or in case of a pileus between abhymenial layer or cortex and subhymenium. The trama may consist of more than one layer (when there is a rather abrupt change in either density, gelatinization or type of hyphae)
e. cortex (cutis, cuticle), dense layer, usually consisting of specialized thick-walled, coloured or gelatinized hyphae, from which abhymenial hairs may be produced; it is only present in the pileus
f. abhymenial hairs, which may be highly variable in colour, width, shape, thickness of wall and length. They may disappear completely with age (glabrescent) or partly (zonate), but zones can also consist of various types of hairs
A second type of layering is formed by the production of a new subhymenial and hymenial layer on the old one, usually after a period of unfavourable climatic circumstances. The phenomenon is often referred to as perennial, but several hymenial layers may actually be produced within a single year.
II. Basidiome texture
1. Texture loose, subicular layer absent or scant, hymenium often not continuous:
a. arachnoid (araneose, cobwebby), consisting of delicate hairs, relatively loose and low
b. byssoid (byssaceous, cottony), consisting of delicate fibrils, somewhat denser and higher than the former
c. hypochnoid (mucedinoid, tomentose), consisting of relatively densely arranged fibrils, more felty than arachnoid or byssoid; sometimes the term 'floccose' is also used for a comparable texture
2. Texture, at least trama and subiculum rather loose, hymenium continuous, except sometimes when young:
a. pellicular (athelioid), with very scant subiculum and trama and usually non-thickening hymenium; hymenial layer separable, often in relatively large pieces
b. membranaceous, with denser trama and/or subiculum, and usually thickening hymenium; hymenial layer usually separable
3. Texture rather dense to dense, hymenium thickening
a. pruinose (subinvisible, forming a thin film), subiculum and trama very thin to practically lacking, hymenium not separable; basidia often lateral
b. ceraceous, with dense, soft hymenium, trama rather loose to usually dense, in the former case hymenial layer may be separable; hyphae thin- to thick-walled, but more gelatinized than tough
c. gelatinous, with dense, soft hymenium and trama; hyphae gelatinized or embedded in gelatinous matrix; when dry the structure becomes cartilagineous
d. crustose (crustaceous), hymenial layer often relatively thin, trama rather loose to rather dense, consisting of firm- to thick-walled hyphae, somewhat tough.
e. coriaceous (leathery), trama and/or subiculum dense and relatively thick, thick-walled hyphae often present. When thick they are sometimes called 'corky'
f. carneous (fleshy), trama and/or subiculum dense, thick, soft, consisting of rather thin-walled or wide hyphae; when dry it may be brittle
A basidiome is called 'separable' when either the subiculum or the trama is loose and the hymenium coherent; either the hymenium or most of the basidiome then comes off in relatively large fragments.
The terms 'farinose' and 'pulverulent' are sometimes also used to describe a basidiome, but actually refer to the hymenial surface and are treated there.
III. Basidiome shape
1. Not pileate or pileus attached over (nearly) maximum width:
a. globose, sphere-shaped
b. tuberculate (tubercular, tuberculiform) - wart-like or knob-like, forming a more or less semiglobular structure
c. pustulate (cushion-shaped), forming a structure with elevated, abrubt margin
d. circular (orbicular, round) fully attached, often concrescent to become effused
e. effused (resupinate), strictly following the substrate; however, when the subiculum is well-developed, the margin may become loose and sometimes recurving when old
f. effused-reflexed, with a pileate part as wide as the resupinate part, and usually rather narrow
g. dimidiate, semicircular
2. Pileate, width of attachment distinctly narrower and gradually widening towards maximum pileus width, not stalked or attached by a narrow point only
a. ligulate (liguliform), strap-shaped
b. spathulate (spathuliform), spatula-shaped, oblong with attenuate base; petaloid or petaliform is a special case
c. cuneate (cuneiform), wedge-shaped
d. flabellate (flabelliform), fan-shaped
e. pseudoinfundibuliform, nearly closed structure originating from inward curving margins of flabellate basidiome
f. infundibuliform, funnel-shaped; cochleate is a special form
3. Attached with a narrow, more or less circular point or stalked
1. umbilicate, attached with a central depression, flat funnel-shaped
2. umbonate, attached to the substratum by a small, boss-like structure (umbonate in general also means a boss-like projection in the centre of an agaricoid pileus)
3 frustulate, forming an elongate wart-like to more or less obconical structure, or better a composed 'basidiome' consisting of a number of these structures, which may be (partly) concrescent
4. discoid (disciform, patelliform, pateriform) - a flattened disc, centrally attached (patelliform and pateriform are usually used for larger basidiomes with slightly upturned margins). The term cyphelloid (to be avoided) means patelliform as Cyphella, but term originating from lichens, meaning a pit in the rind under the surface of the thallus.
5. cupulate (cupular), cup-shaped
6. cyathiform, cup-shaped with flaring margin
7. campanulate (campaniform), bell-shaped, with a constriction or with flaring margin
8. reniform, kidney-shaped, with small stipe
IV. Shape of margin of basidiome
1. Basidiome effused, margin adnate
a. indistinct, hymenium covering nearly all of the basidiome surface
b. arachnoid, thin, loose
c. cottony, somewhat elevated, rather loose
d. fimbriate, fibrillose, with relatively narrow strands
e. rhizomorphic, with distinct hyphal strands (cordons or rhizomorphs)
2. Basidiome pileate, margin free
a. entire, even, not lobed
b. lobed, sinuous in the same plane as that of the basidiome
c. undulate, sinuous in a plane perpendicular to the pileus surface
d. fringed, lacerate (laciniate), marginal aerea frequently split
e. divided, basidiome segmented until half of the total length
f. multifid, basidiome segmented over most of its length
Remark: pileate basidiomes may become concrescent or imbricate, which includes both broadly attached (superpositioning) and narrowly attached to stalked species (forming rosettes or branching with pileoli).
V. The hymenial surface
1. All structures completely covered with hymenium, no sterile apices present
a. even, surface smooth, although it may appear pruinose or pilose
b. tuberculate, warted, with low, often irregular warts, completely covered with hymenium
c. colliculose, with rounded to subconical warts, completely covered with hymenium
d. folded, with ridges, completely covered with hymenium
e. phlebioid, covered with elongated warts or ridges, not or rarely anastomosing
f. merulioid, covered with anastomosing ridges, up to irregularly poroid, ridges often of different heighth, reticulate when dry
2. Hymenial protuberances with sterile apex
a. grandinioid, with low, small, hemisphaerical to short-conical granules, up to 0.1(-0.2) mm high
b. odontioid (sometimes erroneously odontoid), with short, conical to short-cylindrical aculei, up to 0.5 mm high
c. hydnoid, with relatively long, cylindrical spines, 0.5->10 mm
d. raduloid, with relatively thick, entire, flattened, tooth-like structures
e. irpicoid, with irregular, flattened, tooth-like to imperfectly poroid structures, often laciniate
f. poroid, with regular to irregular pores
g. labyrinthoid, with irregular, longitudinal pores or lamellae with irregular anastomoses
h. lamellate, with lamellae
i. epitheloid, with completely sterile more or less cylindrical protuberances
The presence of sterile structures in the hymenium may also have an effect on the appearance of the surface: dendrohyphidia make the surface pruinose to farinaceous, long, thick-walled cystidia make it pruinose to pilose, or even slightly velutinous. When old or dry a thickening hymenium may become rimose (cracked), splitting along the vertical elements, exposing the trama or subiculum.
The configuration of the hymenial surface is highly variable in the resupinate fungi. It has often been considered as an important character, but it has become clear, that transitions from one type to another require little adaptation from the fungus. For example, in the aphyllophoraceous fungi the transition from hydnoid or raduloid to poroid has independently occurred more than ten times (not exhaustive):
1. from even to hydnoid to poroid: Hyphodontia-Schizopora, Phlebia-Mycoacia-Hapalopilus, Tomentella-Tomentellago-Lenzitopsis, Hymenochaete-Hydnochaete-Phellinus, Coniophora-Serpula-Gyrodontium-Boletales
2. from hydnoid or irpicoid to poroid: Irpex-Junghuhnia, Cristinia-Sulphurina (Lindtneria, Stecchericium-Wrightoporia, Trichaptum, Sarcodon-Boletopsis, Trechispora
VI. The pileus surface
a. smooth, no tomentum
b. velutinous, with dense, short straight hairs of equal length
c. pubescent, soft woolly, with dense, short, more or less interwoven hairs of different length
d. felty, with long, appressed hairs forming a dense, packed mat
e. tomentose, woolly, with dense, more or less interwoven hairs of different length
f. fibrillose (hirsute, villose), woolly with interwoven broad hyphae or narrow hyphal strands or aggregates
g. strigose (hispid), with coarse, thick, long, stiff hairs or hyphal aggregates
h. spiculose, with aggregates of hyphae causing a spiny appearance or with antler-like processes
i. squamulose, with aggregates of hyphae causing a scaly appearance
j. glabrescent, becoming smooth with age
2. Irregularities of the surface
a. smooth, no surface roughening
b. pustulate, with pimple-like or blister-like elevations
c. scrobiculate (furrowed, pitted), with ridges, wrinkled, usually radiately
The surface may be or become zonate, either by the occurrence of different types of tomentum or because of glabrescence, which can also result in a diaphanous (semi-transparent) pileus.
VII Trama types
A difference is made between the hymenophoral trama and the pileus and/or stipe trama. In case of resupinate species, everything between the substratum and the subhymenium is considered hymenophoral, except when a distinct layer parallel to the substratum is present, which may be homologous to a pileus trama. In non-resupinate species the trama of spines, dissepiments etc. is considered hymenophoral, together with the often poorly delimited downmost layer of the pileus.
There are two basically different ways to come to a relatively large and firm basidiome: the tough type with strongly interwoven thick-walled hyphae and the fleshy one in which inflated hyphae constitute a substantial part of the trama.
The pileus and stipe trama is sometimes duplex, due to a different compactness and sometimes also a different direction of the constituting hyphae. Zonations may also be present; these may be caused by either a more abundant concentration of ectracellular pigment or more compactly arranged hyphae.
Hyphal strands or cordons consist of parallelly arranged generative and sometimes also skeletal hyphae. There may be a differentiation in medulla and cortex.
I. Dispersed development: hyphae emerging individually from the substratum: the resupinate to dimidiate series.
In this series four (or more) layers form the basidiome: the subiculum, a basal layer of subiculum); the trama or context, the layer perpendicular to the basal layer (or irregular, intricate or subdivided, for example duplex) ; the subhymenium, a usually thin layer giving rise to the basidia, and the hymenium, consisting of basidia (when the hymenophore produces surface-expanding structures, as for example spines or gills, the trama of these structures is called hymenophoral trama). The presence, size and structure of these layers determine the texture of the basidiome, as can be illustrated by some types occurring in resupinate species:
Several subtypes can be distinguished:
(a) the arachnoid type. A subiculum is absent (individual hyphae emerging directly from the substratum support a cluster of basidia) or a very scanty, consisting of a few scattered basal hyphae. The trama is a very loose structure, producing an often non-continuous subhymenium; even the hymenium is not necessarily continuous. The basidiome is very fragile and a thickening hymenium will not easily occur.
(b) the thin-ceraceous type, with a very thin, compact subiculum (often 1–3 hyphae thick), a gelatinized trama consisting of irregular, intricately interwoven hyphae, which directly produce basidia (the subhymenium is lacking).
(c) the membranaceous type, in which the subiculum may be nearly absent to distinct, a well-developed, but not very compact trama and a compact subhymenium and often thickening hymenium.
A stronger development of the parallel layer on the substratum (often combined with a more compact trama), allows for a certain independence of the (generally vertical) substratum. The basidiome can become effused-reflexed (stereoid). The development continues with a reduction of the resupinate part (the reflexed part is much more efficient in spore dispersal and the possibilities of the hymenium to develop secondary surface-enlarging structures are much better), resulting in broadly attached, rather thin basidiomes. In order to maintain a vertical position, the trama needs strong hyphae and a good coherence, as provided by skeletal and binding hyphae. The shape of the basidiome mainly changes around the point of attachment. This may become narrower, finally leading to a stipitate basidiome. This can be illustrated by the following series in Stereum: the resupinate S. rugosum, the effused-reflexed S. hirsutum, the flabellate S. ochraceoflavum and the dimidiate to pseudoinfundibuliform S. ostrea.
Because of gravity, the maximum size for a flat structure is limited, especially when the hyphae are relatively heavy (often thick-walled). Enlargement of the primary spore-producing surface can only be reached by strengthening the point of attachment which results in thicker basidiomes.
A similar line of development is observed in soil or root-inhabiting fungi (horizontal substratum), which is illustrated by the genus Thelephora. The main difference with the vertical substratum is the possibility of a central stipe, and thus a larger and more symmetrical (balance, laws of statics and influence of gravity) basidiome. The Thelephoraceae form principally flattened structures, which, however, in one series develop into clavarioid forms (another way to arrive there!). Thelephora terrestris may be completely resupinate, but can also form more or less spathulate basidiomes; Th. pseudoterrestris is effused-reflexed, Th. aurantiotincta is flabellate and Th. caryophyllea stipitate-infundibuliform. It should, however, be realized, that hyphal fascicles are common in this order, and that the difference between this and the following type can be gradual.
2. Concentrated development: hyphae arising in fascicles from the substratum.
Starting from a fertile pustulate basidiome, the development can be a series from cylindrical to infundibuliform. The pustule forms a stipe, resulting in a more or less capitate he upper and/or middle part, with no sharp distinction between fertile and sterile part: no distinct hymenophore s.str. This structure can become clavate, or even truncate. The delimitation of the hymenophore in the lower parts remains indistinct, but in phototropic (negatively geotropic) species the hymenium tends to disappear or not to develop on a flattened apex. The structure may become excavate and finally hollow, resulting in an infundibuliform basidiome. An example of this series can be found in the Gomphaceae: the acerose Clavariadelphus junceus, the narrowly clavate C. fistulosus, and the broadly clavate C. pistillaris, the truncate Gomphus clavatus and the infundibuliform Gloeocantharellus, or in the Dacrymycetaceae, with the pustulate Dacrymyces deliquescens, the spinulose Calocera cornea, and the branched C. viscosa. Although the hymenophore may follow various lines of development, in an upright structure the possibilities are limited, generally to warts, folds or ridges, depending on the angle of the hymenium with the main axis.
It can also result in a pustulate to tubular series (often geotropic or negatively phototropic), which may start with a pustulate-discoid structure erupting from the surface of the substrate and result in a cup‑shaped or effused‑circular basidiome. This may either fuse with neighbouring basidiomes (the growth is open centrifugal with radiating hyphae and thus the fruitbodies display haptomorphosis) resulting in an effused basidiome, or the basidiomes are so far apart that they remain discrete, more or less circular (or different when the substrate or other environmental factors (e.g. twigs, or unfavourable exposition, or the presence of other fungi) inhibit growth in certain directions) and effused, or, when the subicular layer is well developed, loosen from the substrate (or stay free from it) to form a discoid to cupulate basidiome; such a basidiome may even be minutely stalked. This is expressed for example in Xylobolus frustulatus or Aleurodiscus disciformis, which are very short-stipitate, with the stipe more or less centrally attached at the abhymenial side; a larger example is Cytidia salicina. A number of these basidiomes may fuse to form a resupinate structure, or a basidiome may develop into a disc with elevated margin, as in A. amorphus, or, more extreme, the large, saucer-shaped A. vitellinus. The next step is the cupulate Cyphella digitalis.
A similar series is known in the agaricoid cyphellaceous fungi with the discoid Flagelloscypha minutissima and goes through the cupulate Rectipilus fasciatus to the cylindrical Henningsomyces candidus. Another line of development is the stromatoid Stromatoscypha fimbriata, which can be considered as gregariously growing Rectipilus produced from a subiculum. Fistulina hepatica is another stromatic species. A related series is shown in Auriculariopsis and Schizophyllum, which start discoid but display an asymmetrical development when the basidiome is orientated towards the light. One side grows out, curves over the original disc and develops a geotropic hymenium (Stalpers, 1988).
A second possibility is the development of sterile fascicles, which later produce a subhymenium and hymenium, which then as a rule is perpendicular to the growth direction of the fascicle. The result is a structure with a sterile apex; in its simplest form it is clavarioid, but it can develop along similar lines as the example in the Gomphaceae: truncate to infundibuliform and even agaricoid as seen in Polyporus and Pleurotus.
The larger attachment areas open the possibility of other supporting structures: instead of thick-walled linear structures, swollen cells can also serve to strengthen the basidiome. Such structures contain much water and are thus never perennial (resistant against neither drought nor frost). On the other hand, the fungus need not invest much material, as most of the structure consists of water. This occurs for example in Laetiporus sulphureus or Hericium erinaceus. There are certain parallels with the development of the hymenophoral trama (Reijnders & Stalpers, 1992)
3. Complex basidiomes
The above examples only contain species with simple basidiomes. In reality the picture becomes blurred by parallel, unrelated developments. One of these is the superposition of basidiomes (any kind of branching), another strategy for surface enlargement within a limited space. Imbricate structures represent superposition of sessile (or minutely stalked) basidiomes, while branching as currently understood implies the superposition of stalked (or cylindrical) basidiomes; the development of several basidiomes from a sclerotium or sclerotioid body is here also considered as superposition. Fission and laceration are not considered as branching, contrary to the development of several pilei from a resupinate part (Stereum, Antrodia). All above-mentioned types, except the resupinate one, are capable of superposition, but the strategy is more successful in phototropic than in positively geotropic species.
In order to develop a pileus (be it cupulate or effused‑reflexed) the abhymenial (subicular) layer has to be parallel to the substratum. It also has to protect the basidiome against drought, a function which in resupinate species normally is performed by the substratum (if at all). This is either accomplished by a hard consistency (thick‑walled hyphae, relatively thick subiculum) or by a ceraceous consistency (often with thick‑walled hyphae which are either gelatinized or embedded in mucus) or sometimes by a combination of both (duplex structure).
The hymenium generally is ceraceous, even in species with a hard consistency. It is always a relatively short-lived structure as it consists of thin-walled hyphae only, and the basidia collapse after spore dehiscence. This allows for flexibility (new basidia are easily inserted).
Lateral basidia are often correlated with the lack of a subhymenium. The development of a perpendicular layer usually starts with with the production of lateral cells. Lateral basidia are such cells, and these are also found in for example the young hymenial stages in Athelia, Bondarzewia, Laetiporus, Albatrellus and Fistulina, when a subhymenium is still lacking; further development of basidia will result in a usually very narrow secondary subhymenial layer.
The opposite need not be true: basidiomes lacking a true subhymenium need not have lateral basidia (there can be a septum at the base of the perpendicular branch). Typical catahymenia do not have a subhymenium, at least not in the early stages. The basidia develop individually from the hymenophoral trama, and are often utriform or urniform. This is seen in most species of Vararia.
A catahymenium has sterile structures and lacks a subhymenium. This structure is not sharply delimited from a euhymenium, because a subhymenium may develop secondarily. The interpretation of the basidiome of for example Xenasmatella with a thin basal layer and a thin gelatinized trama is difficult; it can be regarded duplex, or a catahymenium without sterile structures.
II. Microscopic characters
The hyphal system of the aphyllophoroid hymenomycetes can be monomitic, dimitic or trimitic. It is not unusual, that principally monomitic species are called dimitic, because also generative hyphae can mimic skeletals by becoming thick‑walled to nearly solid; when such species are devoid of clamps or display irregularly distributed clamps, it is impossible to apply the criteria of hyphal analysis, as all kinds of intermediates also occur; the thick‑walled (or skeletoid) hyphae are certainly different from skeletal or binding hyphae as encountered in Trametes. In descriptions the terms should be accompagnied by a proper description of the characters of the hyphae, and in taxonomic concepts no dogmatic rules should be adopted (for example that monomitic and dimitic species must not be classified in the same genus). The terminology used here is adopted from Lentz (1954), Talbot (1954) and Donk (1964)
1. Types of hyphae
a. Undifferentiated generative hyphae with thin to thickened walls; local wall thickenings or local inflations may also occur. When very thick-walled and devoid of clamps, they may become indistinguishable from skeletal hyphae (skeletoid hyphae).
b. Skeletal hyphae are terminal ends of generative hyphae, of indeterminate length, thick-walled, unicellular. they are found in the trama and subiculum, and also in hyphal strands. They give rididity to the basidiome.
c. Binding hyphae: branched terminal ends of generative hyphae of determinate length, thick-walled, (usually much-) branched. They provide coherence to the basidiome. Special forms are dichohyphida, effused to concentrated dextrinoid binding hyphae, which may also protrude into the hymenium (see below).
c. Gloeoplerous hyphae, which are thin- to sometimes thick-walled and typically staining in cotton blue. These structures show a wealth of variation (see below).
2. Distribution of clamps
At least in the larger genera all of the following patterns in the distribution of the clamp connections can be found:
a. Clamps present on all primary septa, including subicular, subhymenial and subbasidial ones.
b. Clamps present on the base of the basidia and on most subhymenial hyphae, but lacking at many to nearly all septa of the subiculum.
c. Clamps lacking at the base of the basidia and in the subhymenium, but occurring at some subicular septa.
d. Clamps absent from all septa.
Donk (1956b, 1964) defined hyphidia as: "sterile elements produced by the hyphae of the context (trama) and retaining their hyphal nature by not becoming more or less characteristically inflated, as basidial homologues and other hymenial elements do and to which the term cystidia is generally restricted. Typical hyphidia are produced in advance of the first basidia and form a superficial layer that gradually becomes converted into a catahymenium". Defined this way (especially by the exclusion of inflated structures), the term is not useful, as there are all kinds of transitions between hyphoid and inflated structures. There is a general consensus that the term "paraphyse" (and the suffix ‘-physis’ in general) should be restricted to the ascomycetes, but not on the replacing terms, which have been used for basidiomycetous structures: paraphysoids or paraphysoid hyphae occur frequently in the literature beside hyphidium or simple hyphidium. This is rather unfortunate, as there are transitions between all kinds of hyphidial types as well. Here the terms hyphidium, dendrohyphidium, acanthohyphidium will be used, in a wide sense to also include more swollen structures.
Also it is not deemed necessary for a hyphidium to be produced before the basidia. It seems, that the production of hyphidia continues untill the basidia mature, and that a cell untill a late stage can "decide" to become a basidium instead of a sterile structure (acanthobasidia, basidia with dendroid protuberances) or vice versa. This decision may very well be triggered by environmental factors. This means that hyphidia can be strictly hymenial as well (e.g. Terana, Stereum).
Three types of hyphidia have been distinguishes: simple or haplohyphidia, which are unbranched (or very rarely so), dendro‑ and dichohyphidia which are sparsely to strongly branched (branches generally of very restricted length, but especially in dichohyphidia branches may become so long that the structure as such is hardly (or not) recognizable as a hyphidium) and acanthohyphidia which are not or hardly branched, and at least apically covered with protuberances.
a. Acanthohyphidia are characterized by short, often spine‑like protuberances in at least the apical parts of the structure. The simplest form is found in e.g. Stereum rugosum; it is thin‑walled, isodiametrical and with only a few protuberances (when there is only one, it may be called an acutocystidium) and when the structure is (secondarily?) hymenial, it is sometimes called acanthocystidium. In Xylobolus frustulatus, for example, the acanthohyphidia become thick‑walled (and somewhat coloured) and are aculeate over a longer distance; in mature specimens some are strictly hymenial (although they can also be found deeper in the trama and between the abhymenial hyphae) (Hjortstam et al, 1988). However, the "hymenium" of young basidiomes consists only of similar structures, which there have to be called acanthohyphidia. This cumulates in the structures of Aleurodiscus mirabilis, where the acanthohyphidia are thick‑walled and long (up to 150 um), the protuberances relatively long, and the acanthohyphidia on the abhymenial surface are nearly dendrohyphidia. There are also acanthobasidia and inflated acanthohyphidia (Boidin et al., 1985). In other species inflated (subclavate) acanthohyphidia occur as frequent as cylindrical, narrow acanthohyphidia. Aleurodiscus farlowii for example has thick‑walled cylindrical acanthohyphidia, thin‑walled clavate acanthohyphidia and inflated thin‑walled acanthohyphidia terminating with thick‑walled, cylindrical aculeate prongs (Lemke, 1964). Moreover, such prongs are occasionally also found on basidia. Species like Aleurodiscus fruticetorum, A. spiniger and A. delicatus mainly (or only) display clavate acanthohyphidia; nevertheless these species have a catahymenium.
There are also transitions towards dendrohyphidia: Aleurodiscus botryosus, A. dendroides and Acanthophysium thoenii are good examples. Their branched acanthohyphidia (or aculeate dendrohyphidia) are sometimes called botryophyses (Boidin et al., 1985).
b. Dendrohyphidia are characterized by relatively short, and dense branches in at least the apical parts of the structure. The simplest form is found in e.g. Radulomyces confluens or Epithele typhae; it is thin‑walled and has one to three sidebranches (when there are none, which also occurs in the same species, it is called a simple hyphidium). Dendrohyphidia may become densely branched (e.g. Dendrothele griseocana), and/or originate from a swollen basidiole‑like cell (e.g. Dendrothele alliacea); from this it is a small step towards true basidia, which occasionally are adorned with dendrohyphidia, for example Terana caeruleum).
Dendrohyphidia may become thick‑walled and coloured (e.g. Peniophora versiformis), or encrusted (e.g. Peniophora lycii), or combinations of these. In Cytidia salicina the dendrohyphidia stain in sulphovanilin, and Eriksson et al. (1978) note both cystidia and gloeocystidia terminating in dendrohyphidia in Peniophora lycii. Coloured and thick‑walled dendrohyphidia may be confused with dichohyphidia, which are typically dextrinoid and have stiff branches, but especially the latter character is not always distinct.
3. Dichohyphidia are structures, which are often considered as characteristic for the Lachnocladiaceae, and typically consist of an apically one or more times dichotomously branched hypha which is dextrinoid. They are produced before the basidia and thus may develop a catahymenium. Boidin & al. (1980) give an overview of the variation displayed by dichohyphidia. It is a terminal cell, thin‑walled and hyphoid at the base (which is then called 'stipe'), becoming more thick‑walled near the apex, where the di‑ or trichotomously branching starts; however, in certain species also the basal part becomes thick‑walled and dextrinoid and is then called 'trunc' by Boidin & al. (1980). The length, angle and rigidity of the branches are used to distinguish the following types:
a. geometrical type: a thin‑walled stipe apically branching at angles of about 120 degrees; branches becoming narrower and typically shorter, the ultimate ones being the shortest and narrowest, rather stiff and strictly dichotomous. The outline of the branched part is more or less globose. Examples: hymenial dichohyphidia of Vararia investiens, V. intricata.
b. coralloid type: as the geometrical type, but the apical branches are denser and shorter, but remain stiff. The outline of the branched part is more or less globose. Examples: V. gracilispora, Lachnocladium tubulosum
c. capillary type: as the geometrical type, but the ultimate branches are long, thin and not rigid. The outline of the branched part is more or less globose. Examples: V. minidichophysa, V. fibra.
d. racemose type: branching hardly recognizable as dichotomous, ultimate branches obtuse, the whole structure may resemble a dendrohyphidium. The outline of the branched part is rarely more or less globose, more often there are no downward pointing ultimate branches. Sometimes the branches are not dextrinoid. Examples: V. calami, V. mediospora.
e. filiform type: all branches are long, the stipe is often difficult to detect, there is no rigidity and the outline is not globose. Examples: lower dichohyphidia of V. ochroleuca, V. investiens.
The filiform type gradually merges into the dextrinoid binding hyphae of Scytinostroma. Outside the family they merge in the dextrinoid binding hyphae of e.g. Wrigtoporia, Heterobasidion and Ganoderma, where the dichotomy is even less distinct or completely lost, but which are merely extremes (and thus homologues) of the same basic structure. Dextrinoidity is not constant here (many species of Ganoderma) and may disappear completely. It is not unlikely that the arboriform binding hyphae of e.g. Polyporus are also derived from these hyphae. Compare also Actiniceps and Faerberia. The dichohyphidia of Vararia abortiphysa resemble both the thick‑walled, branched 'cystidia' of Actiniceps as the elements of the hymeniderm of Ganoderma chalceum (see Corner, 1983).
The branching of dichohyphidia is often more compact and the structures are usually smaller near or in the hymenium and looser and larger towards the substratum. There are also cases in which the hymenium is devoid of dichohyphidia.
A special form of dichohyphidia are asterohyphidia. Although extreme forms give a completely different impression, asterohyphidia are only a variation of dichohyphidia (intermediates have also been called ‘stellate dichohyphidia’), This is probably best illustrated by Eriksson (in Hallenberg, 1985), whose drawing of a dichohyphidium of Vararia gallica (Fig. 31c) cannot be distinguished from an asterohyphidium of Asterostroma laxum (Fig. 6b). These asterohyphidia do not branch
from a central point (they hardly ever do, but the branching can be very compact), but the dichotomous branching is rather dense, and the terminal branches are relatively long; there is only very rarely a terminal bifurcation. from a single point) and the larger and more thick-walled the terminal branches are, the more differentiated is the asterohyphidium. As in dichohyphidia, the structures tend to become larger, but in contrast the Especially these structures are sometimes called ‘stellate dichohyphidia’. The more compact the branching (the most compact impression is given by many arms arising branching is hardly less dense, thus making the ‘asteroid’ or ‘stellate’ aspect even more distinct (e.g. Asterostroma cervicolor).
The development of the asterosetae in Asterodon ferruginosus Pat. is quite different (although Corner himself does not concur), and for this structure the term ‘asteroseta’ has been retained. An asteroseta develops from an unbranched seta, from whose base a number of branches sprout; The fully developed structure usually has a distinct main axis, the original seta. This seems to be the reason why Donk (1964) considered Asterodon to belong to the Hymenochaetaceae and Asterostroma to the Lachnocladiaceae, an opinion which has been confirmed by ultrastructural studies. Branching setae or setal hyphae occur in other species of the Hymenochaetaceae, for example in Inonotus cuticularis, or Hymenochaete. [p.12]
The dextrinoid reaction is not always recognizable in dichohyphidia or asterohyphidia, especially with brown hyphae. To improve the recognition, the material is pretreated in saturated ammonia overnight (15–20 h) at 60° C, followed by staining in Melzer’s reagent in 10% acetic acid (AMA). This reaction has not been used widely outside the Lachnocladiaceae, and after more extensive use more species of Aphyllophorales will probably be found to have dextrinoid structures.
4. The gloeoplerous system
Gloeocystidia are sterile cells with dense, staining, oily, resinous or granular contents. They may originate anywhere in the basidiome, are often embedded, but may extend into and even project beyond the hymenium (Price, 1972). Gloeoplerous (gloeocystidial) hyphae are hyphae with contents similar as in gloeocystidia, but in the hymenophoral trama growing perpendicularly to the hymenium (when present in the pileus trama, they may grow in any direction) ; they may curve toward the hymenium to become gloeocystidial and even reach the hymenial surface and protrude beyond it.
A number of terms are used in connection with the gloeoplerous system:
Conducting elements: latex containers, fat containers. Talbot (1954) included latici-ferous and sanguinolentous hyphae in this category.
Coscinoids: long, brown, aseptate hyphae with a pitted, sieve-like surface and a sponge-like interior (Singer, 1986). Only known from Boletales.
Laticiferous hyphae: gloeoplerous hyphae that contain latex. Particularly known from Lactarius and Russula, also reported from Mycena and Lentinellus.
Macrocystidia: gloeocystidia that react positively with sulpho-aldehydes (Romagnesi, 1944).
Oleiferous hyphae: long, rather slender, unbranched to much-branched, typically with oily substance. Many transitions to laticiferous hyphae occur.
Pileogloeocystidia (dermatogloeocystidia) : gloeocystidia in pileus trama or near abhymenial surface (Lohwag, 1941).
Pseudocystidia: hymenial extensions of the gloeoplerous system, sometimes also including all excretory cells in the hymenium as well as ‘homologous cystidia with chemically heterogeneous contents’. Singer (1986) included lacteocystidia (with latex), gloeocystidia (metachromatic oily contents in cresyl blue), chrysocystidia (containing amorphous bodies, generally yellowish in KOH), phaeocystidia (weakly dextrinoid, brownish, containing ‘coelosphaerites’), coscinocystidia (with sponge-like body and/or sieve-like surface), metuloids (thick-walled, with presumably excretory function, often rising from oleiferous hyphae) and oleocystidia (excreting a resinous encrustation through thin or thickened wall) in this category.
Sanguinolentous hyphae: hyphae with blood-red contents (or becoming so by subsequent oxidation after damage and exposure to air), as found in e.g. Stereum and Fistulina.
Vascular hyphae, sap hyphae. General term including gloeoplerous hyphae, but also swollen elements and wide hyphae as found for example in rhizomorphs.
Vesicles: swollen tramal structures, some of which are known to be gloeocystidial (e.g. in Gloeocystidiellum and Peniophora).
Gloeoplerous hyphae and gloeocystidia are very well represented in the Russulales, and display a considerable variation, which gives not only clues to relationships, but also a better understanding of the interdependence of morphologically quite different structures.
A typical gloeoplerous system may consist of thin-walled gloeoplerous hyphae filled with refractive hyaline or yellowish material, which grow parallel to the axis of, for example, a spine and then bend perpendicularly into the hymenium to form gloeocystidia (which then are often called pseudocystidia). The contents may or may not show a colour reaction with sulphobenzaldehydes (SA), (a positive reaction indicating the presence of velutinal-esters) and/or KOH. A typical gloeoplerous system is found in, for example, Auriscalpium, Clavicorona, Gloiodon, Creolophus, Hericium and Dentipratulum. In this group a number of morphological and chemical variations occur. The diameter of the gloeoplerous hyphae in Auriscalpium fimbriato-incisum is not very variable along its length, including the apical gloeocystidial part, but in A. villipes the terminal hymenial part may be more than twice as wide (Maas Geesteranus, 1966b, 1971). In species with inflating hyphae, e.g. Hericium or Dentipellis, also the gloeoplerous hyphae may display swellings. Gloeoplerous hyphae usually have a flexuous-cylindrical to clavate or fusoid gloeocystidial end, which can also be mucronate or monilioid, or terminate with a papilla that may or may not fall off during development (schizopapilla). As a rule, the lower cystidia have a stronger tendency to be vesicular than those originating near the hymenium.
A system of pseudocystidia bending into the hymenium can only be present if there is a - preferably conspicuous - layer perpendicular to the hymenium, which is often not the case in corticiaceous fungi (e.g. species of Gloeocystidiellum, Pseudoxenasma, Phlebiella). In these fungi the gloeoplerous system is by necessity confined to gloeocystidia, which, however, originate usually rather deep in the trama. However, also in species which do have gloeoplerous hyphae, short and straight gloeocystidia occasionally occur (e.g. Dentipratulum). Thus it can be expected that in certain fungi only gloeoplerous hyphae or only gloeocystidia have developed, even if a perpendicular tramal layer is present. And indeed, such species exist.
Gloeocystidia produced deep in the trama tend to be vesicular, while those produced in the subhymenium or in the higher regions of the trama are more cylindrical. Fusiform (or fusoid) gloeocystidia can often be considered as originally vesicular structures that continue to grow towards the hymenium. Lower vesicles or lower parts of gloeocystidia tend to become somewhat thick-walled.
Another variation occurs in the thickness of the walls of both gloeoplerous hyphae and gloeocystidia. Normally they are thin-walled, but in Wrightoporia tropicalis the gloeoplerous hyphae (inclusive the gloeocystidial termination) become distinctly thick-walled. In Stecchericium this tendency is so strong, that the gloeoplerous hyphae are called ‘skeletal-like’ (Maas Geesteranus, 1971). In the gloeoplerous system (hyphae and cystidia) of Stereum this tendency also becomes evident.
Some gloeocystidia develop apical or more rarely lateral protuberances. Such a protuberance is always narrow; it may be a schizopapilla, becoming constricted at the base and falling off, leaving a small, hardly visible scar, as for example seen in Auriscalpium vulgare, or it may have a constriction without subsequent dehiscence, or it is just a tubular elongation shows gloeocystidia with, and some already without, schizopapillae, but also one with a tubular elongation). Such protuberances are always produced on parts exposed to the air. Normally (sub) apical, but in culture, where these structures occur in rather loose aerial mycelium, they are often produced directly on the hyphae.
Usually gloeocystidia are terminal structures, but occasionally they can be lateral (bi-rooted), for example in Gloeocystidiellum porosum (Eriksson & Ryvarden, 1975), and also in G. luridum, G. furfuraceum, and in Pseudoxenasma verrucisporum. These species always have thin-walled gloeocystidia, which often are provided with one or more apical or subapical schizopapillae, and, moreover, the species are strictly resupinate and thin; they are not always ceraceous. It is certainly not coincidental, that some of these species also display lateral basidia (pleurobasidia) besides the terminal ones (in Pseudoxenasma lateral basidia may predominate.
The reaction with sulpho-aldehydes (brown, purplish or black when positive, SA+) has been considered to have taxonomic importance (Donk, 1964; Boidin, 1966b). However, the literature contains conflicting data: Boidin (1958, 1966b) found a consistently negative reaction with sulphobenzaldehyde in the Hericiaceae, Hjortstam (1989) noted brownish reactions in the Hericiaceae with sulphovanillin, and Maas Geesteranus (1975) recorded a purplish brown reaction in Hericium spp. with sulphoanisaldehyde. Larsen and Burdsall (1976) tested a number of gloeocystidial species with sulphobenzaldehyde. They got inconsistent results, even variable within the same specimen. Stalpers (1991) recorded negative reactions in Albatrellus, Creolophus, Hericium and, surprisingly, Stecchericium seriatum, while Dentipellis fragilis reacted positively. Larsen & Burdsall (1976) concluded that ‘sulphuric benzaldehyde was found to be extremely erratic in reacting with gloeocystidial contents, making this character, in our opinion, of questionable taxonomic value’, and Ginns & Freeman (1994) also reported variable reactions. The reaction seems to be only reliable with relatively young and fresh material, as the contents of a gloeocystidium may vary with age. When young, the contents are generally homogeneous, but later become condensed, finally resulting in resinous or hard particles, often distinctly darker and no longer reacting with the chemicals to which they were sensitive before. The condition of herbarium material is not only dependent on the state in which is was collected, but also on the period and treatment before drying, the drying circumstances and the use of chemicals before or during storage. The reaction should not be used to distinguish genera; most larger genera contain both SA+ and SA– species (e.g. Vararia, Gloeocystidiellum, Aleurodiscus, Wrightoporia. The gloeocystidia of some species of Vararia show a reaction with KOH: green, yellowish or orange.
Species with lamprocystidia usually either have gloeocystidia or there are related species with gloeocystidia. Most species of Peniophora have both types, most species of Gloeocystidiellum have gloeocystidia, but some have both lamprocystidia and gloeocystidia. Stereum has only gloeocystidia, but Amylostereum and Laurilia have only encrusted cystidia. Nevertheless, the contents of the cystidia of Laurilia is SA+, indicating similarity. Some species with lamprocystidia almost duplicate similar species with only gloeocystidia (e.g. Scytinostroma cystidiatum). Price (1972) studied the development of both gloeocystidia and cystidia in Peniophora nuda and found that near the margin gloeocystidia and cystidia are often lateral. Young gloeocystidia usually have a rounded apex and in young cystidia it is acute, but intermediates are found; these are rounded, slightly thick-walled and have some crystals at the apex. In Hyphoderma puberum she could not predict if a hymenial cell would become an incrusted cystidium, a gloeocystidium or a basidium. From the thick-walled pseudocystidia of Stecchericium to the encrusted skeletocystidia of Gloeodontia is really a very small step. These observations clearly show, that gloeocystidia and encrusted cystidia are related structures and not basically different as suggested by Whelden (1936).
The gloeoplerous system may be so reduced that it is easily overlooked. Pure cultures offer an extra chance on discovery (and to test the SA-reaction), as it may be present in the form of papillae on rather inconspicuous hyphae (e.g. Heterobasidion, Loweporus).
The gloeoplerous system occurs in nearly all species of the Russulalesbut is found also in the Gomphaceae, Sparassis and the species around Phaeolus, Laetiporus and Meripilus; it is present in some species of Galzinia, Tubulicrinis and Sistotrema, in Laricifomes and some species of Tyromyces, in Clavulicium and some other, isolated species. It also occurs in some Ceratobasidiales and Tulasnellales.
Clemençon (1997) distinguished deuterocystidia which are endosecretory cells and alethocystidia without deuteroplasm. This seems to be a rather artificial classification, as there are all kinds of intermediates between the two types. The content of the cystidia varies from distinctly yellowish to subhyaline to hyaline with refractive contents to cystidia with hyaline non-refractive contents, which stain with sulphoaldehydes and thus with clearly gloeocystidial contents to cystidia with hyaline contents staining distinctly with cotton blue (another indication of 'deuteroplasm') to cystidia which do not, but are capable of excreting a liquid droplet. Encrusted cystidia could only produce their crystalline covering through an excretory process.
Types of cystidia:
1. Asterocystidia: thin-walled, acuminate hymenocystidia with apical, stellate mass of large crystals (Resinicium)
2. Lagenocystidia: small, thin- to thick-walled acuminate hymenocystidia with small crystals covering the apical part (Hyphodontia)
3. Halocystidia: thin-walled capitate hymenocystidia, capitate apex surrounded by with large oil drop, sometimes reported to be contained within a cellular structure.
4. Ornatocystidia: thin- to thick-walled hyphoid, acute tramal cystidia, covered with two rows of flattened cystidia (Subulicystidium). (Wu 1990)
5. Lamprocystidia (metuloids): thick-walled, short-fusiform tramal cystidia, which are encrusted over most of their length; they are probably modified gloeocystidia. The term is often used in a wide sense, including all more or less thick-walled encrusted cystidia.
6. Septocystidia: thin- to thick-walled, cylindrical, smooth or slightly encrusted tramal cystidia with several septa, often with clamps. In case of thick-walled cystidia the apex is thin-walled (Amphinema, Hyphoderma, Candelabrochaete).
7. Lyocystidia: thick-walled tramal cystidia with wall swelling or dissolving in 10% KOH
8. Fasciculocystidia: tramal cystidia arising in bundles from the lower parts of the basidiome; the surfacing parts are the widest and are sometimes septate. Often similar or smaller single tramal cystidia are also present (Dacryobolus, Mycoacia, Veluticeps, Scopuloides)
9. Leptocystidia: general term describing thin-walled tramal or hymenial cystidia with hyaline contents that are larger than basidioles/cystidioles which have a size in the range of the basidia. They may be difficult to distinguish from gloeocystidia (if at all), and sometimes also from hyphae or hyphidia.
10. Gloeocystidia (see above)
11. Stephanocysts, echinocysts etc. (Hyphoderma (Burdsall 1969), but also known from Crepidotus, Senn-Irlett 19??). They have been demonstrated to be capable of germination and infection of nematodes (..Mycotaxon)
12. Basidiole: an immature basidium; it is never certain whether it will remain sterile or develop into a basidium.
13. Cystidiole: sterile structure with the size of an immature basidium, often deviating in a more acuminate apex. It may well be a young basidium in which nuclear events went wrong. The number of cystidioles is often variable within the species and may be related with environmental circumstances during the development of the basidiome.
Basidial shape is highly variable in the aphyllophoroid basidiomycetes, and its morphology lays at the base of the classification that emerged in the second half of the twentiest century. The basal shape is probably ellipsoid to short-clavate, as this is the most economic in surface-volume ratio and thus most resistant against drought, and also because the most simple basidiomes have such basidia, while many other types have an ellipsoid or short-clavate state in the development. However, in a hymenium it is more economical to have as many spores as possible per unit hymenial surface, hence clavate to cylindrical basidia are favoured. Dense packing and protective sugars and proteins reduce moisture loss, and a thickening hymenium (insert of new basidia to replace old ones) adds to the advantages of such a structure.
Basidial shape varies from globose to ovoid, clavate or cylindrical, or urniform. The number of sterigmata varies from 1-8, but is typically 4. Branching of the basidia usually is racemose to nearly sympodial, but occasionally it is percurrent (repeating basidia). Basidia are usually terminal, but in some genea birooted basidia are common, or at least an indication of an intercalary development remains present (pleurobasidia).
An urniform or utriform basidium is often explained by assuming a two–phase development, first the production of a vesicular ‘probasidium’, followed by an elongation and production of sterigmata and spores. Urniform and utriform basidia are not produced in thickening hymenia, but often in species with an ‘interspaced’ basidial development (catahymenium and the like). Bi-rooted basidia are mainly produced in species without a distinct subhymenium. In fact they are homologous with the first developing hyphae of a true subhymenium, i.e. the layer perpendicular to the hymenophoral trama. The branches at the base of the development of this layer are generally intercalary and not terminal, as, for example, demonstrated in species of Athelia. Also here the hymenium is never really thickening; as soon as this occurs regularly, true lateral basidia can only be found in young basidiomes.
The strategy to form catahymenia seems to be based on coping with relatively dry circumstances, because it gives the possibility to react fast on the occurrence of favourable conditions. The layer of hyphidia create a space with unmoving air, and thus protection against drought, in which either probasidia (ellipsoid, often somewhat thick-walled cells) or basidium initials wait to develop rapidly under sufficiently moist conditions. The thus formed basidia have a swollen base; they may have a very short to very long narrower median part, and terminate with a slightly to distinctly swollen upper part on which sterigmata develop. Of course, catahymenia are not thickening.
Also euhymenia may form urniform basidia, either under moist conditions and then the basidiome is often loose or as a consequence of another strategy to survive drought: the production of protective sugars and proteins, which form a ceraceous or more typical a gelatinous matrix, from which the upper part of the basidium has to emerge in order to set the spores free in a gaseous environment. This strategy does allow hymenial thickening.
However, the commonest type of hymenium is ceraceous, with narrowly clavate to cylindrical basidia closely packed together (under these circumstances the most efficient shape, as the evaporating surface is confined to the apex of the basidium). This is the most successful strategy for temperate climates, but there are two adaptations to minimize drought damage: the production of projecting hyphidia or cystidia to create a more or less stable layer of air and/or the formation of thick-walled trama with a considerable resistance against both cold and drought, from which a new hymenium can be formed. This opens the possibility of perennial basidiomes (but the presence of several hymenial layers does not implicitly mean that the basidiome actually has overwintered).
The spores are usually thin-walled and hyaline, but the walls may become slightly to distinctly thick-walled and then sometimes also slightly yellowish to brownish. Some spores (e.g. Peniophora) are pink in mass.
There is a certain order in the various spore shapes, although the regularity is obscured by the presence of the apiculus, which supports the asymmetical ballistospore. The ventral side, where the spores face each other on the basidium, is often more flattened than the dorsal side. In the smooth, regular (unlobed) spores several lines of development occur, which also may occur simultaneously:
A. Spores regular, straight, two-sided symmetrical along length and width axis (apiculus excluded)
1. globose 1<Q<1.05
2. subglobose 1.05<Q<1.15
3. ellipsoid 1.15<Q<2
a. broadly ellipsoid 1.15<Q<1.3
b. ellipsoid 1.3<Q<1.6
c. narrowly ellipsoid (subellipsoid) 1.6<Q<2
4. cylindrical 2<Q<4
a. cylindrical 2<Q<3 (the wider are sometimes called subcylindrical)
b. narrowly cylindrical 3<Q<4
5. bacilliform, filiform Q>4
The true fusiform spores, which are attenuate at both sides also belong here, but when it occurs in the homobasidiomycetes, it is more often called turbinate; unfortunately the term fusiform is in the corticiacous fungi often used for another shape, where the largest width is (much) closer to the apiculus than to the apex, which then becomes relatively acute, but is always rounded.
B. Spores regular, one-sided symmetrical (length axis only), because the widest part is closer to the apiculus or to the apex. In the latter case the following terms may be proceeded by the prefix ‘ob’, but this is rarely consequently done. In this text the use of terms like ‘obovoid’ and ‘obpyriform’ is omitted. These terms typically more apply to the dorsal view than the lateral view.
2. pyriform (ovoid and slightly attenuate near the apiculus)
The lateral view is strongly influenced by the apicular area, where the suprahilar plage is usually straight or even slightly depressed, see under D
C. Spores regular, curved, one-sided symmetrical (curve in the middle)
1. reniform (bean-shaped), short cylindrical and distinctly curved
2. allantoid, long cylindrical and slightly to distinctly curved
3. lunate, narrowly cylindrical to bacilliform and strongly curved
D. Spores regular, asymmetrically curved, asymmetrical (curve near the suprahilar plage)
1. amygdaliform (almond-shaped, broadly ovoid and slightly curved near the apiculus)
2. lacrymoid (ovoid and slightly curved near the apiculus) (obliquely ellipsoid)
3. pip-shaped (apple seed shaped, narrowly ovoid, slightly curved near the apiculus)
4. fusiform (very narrowly ovoid, slightly curved near the apiculus)
5. sigmoid, when there are actually two curves, a suprahilar one and a usually stronger, more central one. It can also happen in narrowly fusiform spores.
The shape may become accentuated by a dorsal widening; especially in relatively broad spores this may lead to terms as citriform or biapiculate, and even D-shaped.
A confusing term is navicular, which is used in two ways: fusiform with rounded ends (boat from above) or inequilaterally fusiform, more or less keeled (boat seen from side).
Ornamentation also occurs, and varies from roughened to asperulate, echinulate, or with ridges. Some react with Melzer's, becoming brownish (dextrinoid) or blue (amyloid). The amyloid reaction may be faint and sometimes only greyish.
8. Chemical reactions
A primary distinction is based on the amyloid reaction. Within Vararia s.l. three types can be distinguished: spore wall completely amyloid, only a suprahilar plage amyloid, or spore wall not amyloid. In the other taxa of the Russulales the spore wall is amyloid throughout or absent.
Typically the spores are ornamented and globose to ellipsoid; in Vararia and Scytinostroma a series ranging from pip-shaped to fusoid or sigmoid spores can be observed, as also seen in other groups (e.g. Tubulicium, Albatrellus); this development is usually combined with a loss of amyloidity and ornamentation. In the Lachnocladiaceae and Polyporaceae most species have smooth spores.
Capellano & Keller (1978) and Keller (1979, 1986) studied the spores of the Russulales with TEM. The terminology of the layers differed in every publication, and differences in magnification make a comparison difficult, but there seem to be three layers: the innermost layer is the coriotunica (epispore), a more or less transparent layer that becomes condensed towards the outside (sometimes appearing as a separate layer, more often gradually darkening); the tectum (perispore, podo-stratum) is responsible for the ornamentation and is bordered by a condensed interstratum (which is sometimes also deposited at the inner side of the tectum, especially in spores with a large ornamentation like Bondarzewia) ; the outermost layer is the sporothecium (ectospore), sometimes differentiated into a transparent endosporothecium and an opaque ectosporothecium. The spores of Xenasmatella and Litschauerella are of a different type (Keller, 1986).The ornamentation of Russulales spores dissolves at least partly in KOH.
The only anamorph genus described for the Russulales is Spiniger (Stalpers, 1974), characterized by clavate to rarely cylindrical conidiophores bearing blastic conidia on the apical part, arising simultaneously from conical to cylindrical denticles. Such anamorphs are known from species of Bondarzewia, Dichostereum, Heterobasidion and Laurilia. Outside the order, two other genera have similar anamorphs: Mutatoderma, a segregate of Hyphoderma with gloeocystidia, lamprocystidia and smooth, allantoid spores (probably related to Laurilia and/or Amylostereum) and Resinicium, although the latter deviates considerably from typical Spiniger; it should be classified in a separate genus.
Stalpers (1987) discussed the homology of the conidiophores of Spiniger with basidia and of the conidia with basidiospores, with the following arguments:
1. Conidiophore versus basidium
Corner (1948) distinguished seven stages in the development of the basidium: inception (the preliminary hyphal stage), charging (the filling with cytoplasm), condensation of storage material, initial vacuolization of the full-sized basidium, development of the sterigmata, development of the spores, and discharge of the spores followed by collapse of the basidium.
The first four stages are similar in Spiniger conidiophores and typical holobasidia. Even if inception should include insertion of young basidia in a hymenium, conidiomes of Laurilia sulcata and Heterobasidion annosum show a similar phenomenon.
2. Denticles versus sterigmata
There are some differences in the development of the sterigmata when compared with the denticles of Spiniger; the position of the sterigmata is more or less fixed at a similar distance from each other and from the centre of the apex, while that of the conidiogenous denticles seems to be random (although concentrated in the apical zone). However, there are several reports of a more random position of sterigmata, for example in Phanerochaete chrysosporium (Stalpers, 1984) and more commonly in the gasteromycetes, where even more than eight spores can be produced on a [p. 23] single basidium. The irregularly spaced sterigmata of Exobasidium were for a long time interpreted as conidiogenous denticles.
The development of sterigmata seems to be similar in most major groups of the basidiomycetes. When a basidium has reached its full size, small conical bulbs are produced by the four-layered cell wall, followed by the formation of a tube-like structure, which breaks through the outer two layers. Sterigmata are thus endogenous structures and the sterigmal wall is thinner than that of the basidium. The descriptions given by Cook (1977) and Hanlin (1982) of the formation of conidial denticles in Spiniger meineckellus agree in detail with the development of sterigmata. Also here the initial is four-layered and the denticles break through the outer wall and are two-layered.
The conidia of Spiniger are not violently discharged, while the basidiospores of the agaricoid and aphyllophoroid species are generally ballistospores. However, the development is comparable with that of the statismospores of gasteromycetes, as far as can be concluded from the TEM micrographs of Cook (1977) and Hanlin (1982)
3. Conidia versus basidiospores
Both basidiospores and conidia of the Spiniger type develop synchronously and the nuclei inside the basidium or conidiophore migrate more or less simultaneously into the sterigmata or denticles.
TEM photographs of the walls of spores (Keller, 1973) and conidia (Hanlin, 1982) of Heterobasidion annosum show similar layers.
The shape of the conidia of a Spiniger anamorph is close to that of the basidiospores of the teleomorph; the conidia are more symmetrical (no apiculus) and tend to be somewhat more elongated and narrowed towards the base. Bondarzewia mesenterica has globose basidiospores and conidia, Heterobasidion annosum broadly ellipsoid spores and ovoid to pyriform conidia, Laurilia sulcata subglobose basidiospores and ovoid to narrowly pyriform conidia, and Hyphoderma mutatum cylindrical spores and conidia.
The ornamentation of the conidia is comparable to that of the basidiospores, but less pronounced in the former. The basidiospores of Bondarzewia are strongly ridged, but the conidia are warted or have low ridges; the basidiospores of Laurilia sulcata are echinulate, but the conidia are warted, and the basidiospores of Heterobasidion annosum are warted, but the conidia are (almost) smooth.
The reaction of the basidiospores with Melzer’s is comparable to that of the conidia, but when positive it is stronger in the basidiospores (correlated with the stronger ornamentation) .