Data from CBS Aphyllophorales database

Royoporus pseudobetulinus (Murashk. ex Pilat) De, comb. nov. Basionym : Ungulina pseudobetulina Murashk. ex Pilat, Bull. Soc. Mycol. Fr. 48: 23, 1932.

= Piptoporus pseudobetulinus (Murashk. ex Pilat) Pilat, Atlas des champignons de l'Europe.3 : 123, 1937.

= Polyporus pseudobetulinus (Murashk. ex Pilat) Thom, Kotiranta et Niemela, Mycologia 82(5) : 582, 1990.

Basidiocarp annual, pileate, solitary or imbricate in pairs, attached to the substratum by a narrow base or with a short stipe, pileus at first ungulate, then convex, applanate, semicircular or dimidiate, 4-17 x 5-24 x 1.4-4.5 cm., pulpy to elastic when fresh, coriaceous when dry, upper surface glabrous, azonate with a smooth, thin, peelabte, glossy cuticle, cream, pale straw yellow to light brownish, often with some indistinct radial Unes and with fine brownish to greyish orange fibrils, becoming areolate. Margin acute to obtuse and incurved. Context white to cream, homogeneous, up to 3 cm thick, fleshy, tough and corky on drying. Hymenial surface white when young, yellowish to orange with age and drying, pores angular, often radially aligned, 1-3 per mm, dissepiments thin, pore tubes up to 10 mm long, white to light yellowish orange.

Hyphal system dimitic. Generative hyphae simple septate, hyaline, usuallythin-walled, 2.5-6.0 µm wide, occasionally branched (Fig. 1), in subhymenium very narrow, 1.6-2.5 µm wide and much branched (Fig. 2), in context some slightly thick-walled, infrequently branched and a little inflated, up to 14 µm wide (Fig. 3), on the pileus surface occur some closely interlaced, thin-walled, short-celled, up to 6 µm wide hyphae forming skin-like structure (Fig. 4) and some thin- to slightly thick-walled pale brown mass of cuticular cells (Fig. 5). Binding hyphae hyaline, dendritic, thick-walled, in the context 3-14 µm wide showing wide lumina and usually tapering to 1-2 µm wide whig-like tips (Fig. 6), in trama much branched, frequently subsolid, 1.5-4.5 µm wide (Fig. 7). Basidia hyaline, thin-walled, clavate, with 2 and 4 sterigmata, 18-40 x 5-7 µm, simple septate at the base (Fig. 8). Basidiospores hyaline, thin-walled, smooth, cylindrical to slightly fusiform, apiculate, non-amyloid, 7-10 x 2.5-3.5 µm, sonie wfth one or more guttulae (Fig. 9). Hyphal pegs infrequent.

SPECIMENS EXAMINED : Tervola, Pisavaara Strict Nat. Reserve, Finland, 29.7.1979, Tuomo Niemela and Heikki Kotiranta, TN 1524 and TN 1573. Grey county, Letterbreen, Ontario, Canada, 10.6.1987, R.G. Thom and L.M. Banks, DAOM 198666. Ottawa-Carleton regional municipality, Hwy. 417 at McGee Sideroad, Ontario, Canada, 19.6.1988, R.G. Thom, DAOM 198664.

DISCUSSION

The aforesaid description indicates that P. pseudobetulinus has a dimitic hyphal system wfth generative hyphae and binding hyphae and thus agrees wfth the views held by Nunez and Ryvarden (1995) and Thom et al. (1990). The species lacks clamp connections. I saw only simple septa on the generative hyphae of R. pseudobetulinus and I did not find any clamp at the base of any basidium, i.e., the basidia were simple septate at base. Domanski et al. (1967) and Thorn et al. (1990) did not observe any clamps in this species and there are no clamps in cultures (Thom et al.1990, Stalpers 1978). Thus Nunez and Ryvarden's (1995) report of a clamp connection at the base of basidium may be an error.

This species has been described under Piptoporus Karst. (Pilat 1937, Domanski et al.1967) and Polyporus Adans. : Fr. (Nunez and Ryvarden 1995, Thom et al. 1990).

Piptoporus betulinus (Bull. : Fr.) Karst., the type species of the genus Piptoporus, causes a brown rot (Gilbertson and Ryvarden 1987), whereas P. pseudobetulinus causes white rot (Thom et al. 1990). The evolutionary and systematic importance of white rot versus brown rot has been emphasized by Nobles (1971), David (1980), Gilbertson (1980, 1981) and Redhead and Ginns (1985), and is now generally accepted. Therefore, P. pseudobetulinus causing white rot can not be congeneric with P.betulinus which causes brown rot. Corner's (1984) suggestion that P. pseudobetulinus might belong in Buglossoporus Kotl. & Pouz. is to be rejected for the same reason.

Presence or absence of clamp connections on generative hyphae is an important character in circumscribing genera (Teixeira 1994 p. 32, De 1996, 1997). Therefore, inclusion of P. pseudobetulinus by Thom et al. (1990) in Polyporus, a genus characterised by the presence of clamps in all species, can not be agreed upon.

My study revealed that P. pseudobetulinus exhibits a combination of characters not found in any other existing genus except Royoporus De. Both Royoporus spathulatus (Jungh.) De, the type species of the genus Royoporus (De 1996), and P. pseudobetulinus possess annual, dimidiate, solitary to imbricate, very shortly and laterally stipitate basidiocarps wfth poroid hymenial surface having angular, radially aligned pores; white context; a dimitic hyphal system with hyaline, simple septate generative hyphae and hyaline binding hyphae; hyaline, smooth, thin-walied cylindrical, non-amyloid basidiospores wfth one or more guttulae and cause white rot of angiospermic wood. So many features in conimon suggest a close relationship between R. spathulatus and P. pseudobetulinus.

But there are some differences between R. spathulatus and P. pseudobetulinus. P. pseudobetulinus possesses cream, pale straw yellow to light brownish, smooth, glossy, thin, peelable cuticle at the pileus surface but such cuticle is absent in R. spathulatus. Besides, basidiocarps of P. pseudobetulinus are relatively larger and thicker than those of R. spathulatus. But these exomorphological differences may be considered important only at the species level.

Polyporus pseudobetulinus (Pilát) rhorn, Kotiranta & Niemelä Fig. 16 Mycologia 82:583, 1990. Ungulina pseudobetulina Pilát, Bull. Soc. Mycol. Fr. 48:23, 1932. Polyporus xinjiangensis? Zhao, Zu & Zhang, Acta Microbiol. Sin. 21:430, 1982.

Basidiocarps annual, attached to the substrate by a narrow base; pileus at first ungulate, then convex, dimidiate, solitary or imbricate in pairs, 6-18(24) cm broad and up to 4.5 cm thick, with a deflexed margin; upper surface yellowish-white to greyish-orange, with a thin cuticle and fine brownish to greyish-orange fibrils, becoming areolate; pore surface whitish to yellowish-orange, pores circular, 1-3 per mm, tube layer concolorous with context, up to l cm thick; context white to cream, up to 3 cm thick, fleshy, drying tough and corky.

Hyphal system dimitic; generative hyphae hyaline, thin-walled, 2.5-6 µm wide, in the pilear surface embedded in amorphous matter; skeleto-binding hyphae hyaline, thick-walled, nonseptate, up to 13 µm in diam, many vegetative hyphae unbranched in the upper context. Basidia clavate, 4-sterigmate, 18.5-40.5 x 5-7 µm, with a basal clamp at the base. Basidiospores cylindric to slightly fusiform, (6.5)7.2-10 x 2.5-3.4 µm. Cultural characteristics. See rhorn et al. 1990.

Substrata. On standing dead trunks of Populus spp., usually high above the ground, found on Salix in Japan.

Distribution. From continental areas in Finland, Russia, Japan, and Canada.