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Page number:53 
Remarks (internal):Basidiocarps of Poria alpina are similar in microscopic characteristics to those of P. xantha (Fr.) Cke. They differ in being perennial, thicker and having larger pores. J. R. Weir collected specimens of P. alpina in Montana and identified them as a resupinate form of Fomes officinalis (Vill. ex Fr.) Faull. These are apparently the basis for his report (28) of F. officinalis "often fruiting in Poria-like form." Fomes officinalis is similar to P. alpina in texture, taste, and induced rot, but has ellipsoid to ovoid spores.
Lowe and Gilbertson (15) reported P. alpina from Idaho and Oregon and state that "no fertile specimens have yet been seen." A fertile specimen from Montana was subsequently found in the National Fungus Collections (J. R. Weir No. 10748, on Larix occidentalis Nutt., Columbia Falls, Montana, June 14, 1918).
Baxter (3) apparently considered this plant to be a thick form of P. xantha, described it as P, xantha forma crassa, and reported it as widely distributed in North America. Our specimens, however, agree with the type of P. alpina from Europe and it appears best to use Litschauer's name for this species. Poria crassa (Karst.) Sacc. is a distinctly different species with broadly ellipsoid spores.
Description type:Non-original description 
Description:Poria alpina Litsch., Oest. Bot. Zeit. 88: 143. 1939.
Basidiocarps perennial, becoming chalky and easily crumbled when dry, easily separated from the substratum; margin fertile; pore surface bright lemon yellow when fresh, fading to yellowish-buff or tan when dried, the pores circular to angular, with thin, lacerate dissepiments, 2-4 per mm; context white to cream, chalky, up to 2 mm thick; tube layer yellowish, distinct from context, brittle, up to 1.5 cm thick; taste bitter.
Context hyphae hyaline in KOH solution, mostly thick-walled, aseptate, usually sinuous, 3-5 µm; in diam, others thin-walled, inconspicuous, witli clamp connections, 3-5 µm in diam; tramal hyphae similar; basidia clavate, 4-sterigmate, 10-12 µm; fusoid cystidioles present, 4-5 µm in diam, barely projecting beyond the basidia; spores hyaline, smooth, allantoid, 1 1.5 x 1-1.5 µm; (Fig. 1, C).
Substratum and rot: Associated with a brown cubical rot of Larix and Pinus. The decayed wood often contains flat mycelial felts or masses of white fungus tissue where it has cracked and separated in the decay process.

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