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Remarks (internal):This is the second report of Hyphoderma sibiricum from North America. Martin & Gilbertson (Mycotaxon 6: 61. 1977) reported a collection (RLG 4988, ARIZ) from Colorado which has ovoid spores 6-7 x 4.5 µm, stalked pleurobasidia with short sterigmata (-4 µm) and lacks hyphidia. It is Xenasmatella filicina (Bourd.) Oberw. and not H. sibiricum. The spores of H. sibiricum are typically 4-5.5 µm wide (Parmasto loc. cit., Eriksson & Ryvarden loc. cit.). It was described (Parmasto, loc. cit.) from collections made in central Siberia (Krasnoiarsk and Altai Mountains) on Abies sibirica and other conifers. Eriksson & Ryvarden (loc. cit.) recorded several collections from Fennoscandia on conifer wood especially Picea abies.
The Yukon collection was found to be identical with Swedish collections of H. sibiricum (Ã…ngerman-land, Hjortstam 4290 and Lule Lappmark, on Pinus sylvestris, B. & J. Eriksson 4327, filed as DAOM 172967 and 172966, respectively).
Hyphoderma cremeoalbum (Höhn. & Litsch.) Jul.,. as described in Eriksson & Ryvarden (op. cit., p. 465), is the species most similar to H. sibiricum. Its spores are 10-14 x 5-6.5 µm and, therefore, are distinctly larger than those of H. sibiricum.
Description type:Non-original description 
Description:Hyphoderma sibiricum (Parm.) Erikss. et Strid, in Eriksson & Ryvarden, The Corticiaceae of North Europe, Vol. 3, p. 535. Fungiflora, Oslo. 1975.
= Radulomyces sibiricus Parm., Consp. syst. Cort., p. 223. 1968.
Basidiome: thin (<0.1mm), effuse, in small patches to 1 cm diam; hymenial surface smooth but when dry fissured on older parts, a delicate, dry, crust over a very thin, white subiculum, greyish white to pale cream color; margin thin, white, finely fibrillose-granulose, 0.5-1 mm wide. Hyphae: loosely woven, distinct but rather obscured due to considerable crystalline deposits throughout the subiculum, hyaline, thin-walled, rather frequently branched, with clamps, 2-3 µm diam. Hyphidia: numerous, hyaline, thin-walled, 2(-3) µm diam, cylindrical, some bifurcate at the apex. Basidia: initially a broadly clavate, stalked cell, which apparently elongates apically to produce a suburniform to narrowly clavate cell, 30 x 5-6 µm, with a basal clamp and containing a few to numerous oil drops; sterigmata four, each 5-7 µm long. Basidiospores: broadly ellipsoid with the apices broadly rounded and sides only slightly convex (i.e., nearly parallel), hyaline, thin-walled, smooth, acyanophilous, nonamyloid, 7-8 x 4.5-5 µm, with one large oil drop and a rather broad, blunt apiculus, sometimes adhering in groups of 2-4 spores.
Substrate: Soft, well-rotted, decorticated conifer log 37 cm in diameter.
Distribution: Yukon.
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