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Page number:261 
Description type:Non-original description 
Description:Aleurodiscus penicillatus Burt, Ann. Mo. Bot. Gard. 5: 201. 1918(Fig. 16)
Basidiocarp corticioid, initially in separate patches 2-3 mm in diameter, readily confluent, forming irregularly effused areas; margins at length determinate, adnate. Fructification variable in thickness, 200-400 µm thick in cross section (forms from western North America reaching up to 700 µm thick) ; texture granular-pruinose to compact-pulverulent. Hymenial surface continuous to rimose on drying (often areolate in thicker specimens) ; light buff to cream-buff colored. Context monomitic, composed of thin-walled, branched, clamped, subregular hyphae, 2-2.5(-3) µm in diameter. Catahymenium composed of numerous, thin-walled acanthophyses, ampulliform pseudocystidia, simple paraphysoids, and basidial elements. Acanthophyses cylindrical to broadly clavate, 20-100 x 5-20 µm, uniformly thin-walled; bearing scattered, delicate, acicular prongs mostly toward the apex. Acicular prongs are seen to advantage in Melzer's; individual prongs measure 3-7 µm long and about 0.7 µm wide. Pseudocystidia initially embedded, flexuous-cylindric to emergentampulliform, (35-)50-60(-75) x (9-)10-12 µm, bearing one to several apical gemmae; contents frequently with a conspicuous globoid, hyaline in KOH, not darkening in sulphobenzaldehyde. Hyphal-like paraphysoids simple to branched, (1.5-)2-2.5 µm in diameter. Basidia at maturity clavate, 55-90(-110) x 16-24 µm, thin-walled, often with lateral acicular prongs; bearing (two) four subulate, slightly incurved sterigmata 14-19 µm long and 4-5 µm wide at base. Basidiospores globoid to subovoid, 15.5-20(-25) x (13-)14-19(-21) µm, apiculate, flattened adaxially, walls thickened at maturity up to 2 µm thick, and then bearing opposite germ-pores at the poles of the spore; walls appearing smooth to roughened in KOH, echinate in Melzer's, amyloid. Distribution: Ontario, Quebec, British Columbia; New England, New York, Idaho, Washington, Oregon, California.
Habitat: Effused on the dead branches and twigs of various conifers; occurring principally on Tsuga canadensis in eastern North America and commonly on Pseudotsuga taxifolia and Tsuga heterophylla in western North America. Forms of this species also occur on Picea sitchensis in the Pacific Northwest. Those specimens on Picea sitchensis exhibit a larger average spore range (viz., 22-25 x 15-21 µm).
Discussion: The uniformly thin-walled acanthophyses of this species, bearing delicate, acicular prongs, are found also in A. fruticetorum W. B. Cooke. This latter species, however, is substereoid, dimitic, and possesses smooth spores. The closest relatives of A. penicillatus are probably two European species-A. apricans Bourd. and A. delicatus Wakef.
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