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Page number:243 
Description type:Non-original description 
Description:Aleurodiscus disciformis (DC. per Fr.) Pat., Bull. Soc. Mycol. Fr. 10: 80. 1894. (Fig. 7) Thelephora disciformis DC., Flor. Fr. 6: 31. 1815(devalidated name). Thelephora disciformis DC. per Fr., Syst. Mycol. 1: 443. 1821., Elench. Fung. 1: 189. 1828.
Stereum disciforme (DC. per Fr.) Fr., Epicr. Syst. Mycol. 551. 1838., Hymen. Eur. 642. 1874.
Peniophora disciformis (DC. per Fr.) Cooke, Grev. 8: 20. 1879. = Thelephora castanea Schleich., Mycogr. 3: 216. n. d.
Basidiocarp pulvinate to disciform, broadly attached, in patches 1-3 cm in diameter; margins thick, determinate, often reflexed to slightly incurved. Fructification 500-1000 µm thick in cross section; texture compact-subcoriaceous to coriaceous. Hymenial surface drying a cream to pale yellow-buff, often with cinereous tints; continuous to slightly rimose in age. Abhymenial surface, when exposed, considerably darker in color, smooth. Context monomitic, hyphae ascending, obscured by abundant crystalline granulation, simple-septate, subregular, mostly thin-walled, branched, measuring (1.5-)2-2.5 µm in diameter; basal hyphae subregular with partially thickened walls and scattered clamps, measure 3.5-4.5 µm in diameter. Hymenium composed of moniliform pseudocystidia, basidial elements, and numerous hyphal-like paraphysoids. Pseudocystidia (macrocystidia) thin-walled, often embedded and then collapsed, flexuous-cylindric, 50-80 x (6.3-)7-10(-12) µm, often moniliform with two-eight apical swellings; contents faintly yellowish in KOH, darkening in sulphobenzaldehyde. Simple paraphysoids 3-5 µm in diameter. Basidioles clavate, 45-75 x 8-11 µm, with homogeneous contents. Basidia at maturity cylindrical to subclavate, 60-90 x 10-12(-14) µm, bearing two-four sterigmata up to 18 µm long and 3-5 wide at base. Basidiospores ovoid to ovoid-ellipsoid, (13-)16-18(-20) x (8.5-)11-14(-16) µm, walls firm to thickened up to 1.5 µm, inconspicuously echinulate in Melzer's with spines measuring less than 0.5 µm long, amyloid.
Distribution: Oregon, California; Mexico; Europe; Siberia. An African specimen cited by Talbot (1956, p. 468) as Aleurodiscus disciformis is A. candidus Schw.
Habitat: Mostly on the bark of deciduous wood, usually Quercus.
Discussion: This species is readily segregated from Aleurodiscus amorphus (Pers. per Purt.: Fr.) J. Schroet. on a number of features. Particularly noteworthy, however, are the pseudocystidia in the two species. These elements are linearly constricted or moniliform in both species, but in A. disciformis the pseudocystidia possess macrocystidioid contents that darken characteristically in sulphobenzaldehyde.
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