Agaricus subrufescens Peck, Rep. State Bot.
Index Fungorum number: IF248259, MycoBank: MB248259
Basidiocarp medium to large (Figure 1). Pileus 50-93 mm diam., circular, hemispherical, convex to plano-convex with a flattened disc, edge straight/ appendiculate/ denticulate with remnants of veil, surface dry, covered by fibrillose squamulose hairs, appressed and dense at the centre, less dense towards the margin, purple-brown (6E5)/ reddish-brown (8E4-8E5)/ dark brown (9F6) at the center and purple-brown (6E5)/ reddish-brown (8E4-8E5)/ brownish orange (7C2) towards the margin. Context 4-6 thick at the disc, white, fleshy, cottony. Lamellae attachment free, crowded, with 3-4 series of lamellae, 3-7 mm broad, normal, white/ pink/ brown/ dark brown with age. Stipe 68-95 × 6-12 (base 12-15) mm, upwardly tapering or cylindrical, subbulbous with rhizomorphs, insertion central, pith hollow, surface smooth, with scattered small fibrillose nodules below annulus. Annulus membranous, pendent, superior, white and lost in age. Smell slightly almond. The KOH reaction is negative or yellow. Basidiospores (Figure 2b) 4-6.5 × 3-4.5 μm, ellipsoid, some ovate, smooth, apiculus distinct, without germ pore. Basidia (Figure 2c) 10-19 × 4-8 μm, clavate, tetrasporic, hyaline, smooth. Cheilocystidia (Figure 2d) consisting of 7-18 × 5-13 μm elements, catenulate, hyaline, smooth, spherical or subspherical, 2-4 elements in chains, pyriform in basal element. Pileipellis (Figure 2e) a cutis, composed of 3.75-16.25 μm hyphae, repent in net-like, brown or light brown, smooth, constricted at the septa in most cases. Annulus consisting of 4-7.5 μm diam. hyphae, mostly cylindrical, smooth and hyaline.
Habitat: Solitary or clustered in soil with Bambuseae sp., Dipterocarpus sp. and Samanea saman (Jacq.) Merr. and in flower pot.
Specimen examined: THAILAND, Chiang Mai Province, Mae Taeng District, Ban Pha Deng Village, Mushroom Research Centre, N 19°17.123’ E 98°44. 009’, elev. 900 m., in flower pot, 28 August 2004, K.D. Hyde, ZRL2134 (BBH19514, SFSU); ibid. Mok Fah Waterfall, N 19°08' 43.20" E 98°54' 19.52", elev. 1464m, near bamboo, 25 June 2005, R.L. Zhao, ZRL2036 (BBH19422, SFSU); Chiang Rai Province, Tambon Mae Korn and Tambon Huay Chompoo, Muang District, Khunkorn Waterfall, N19°51-54' E 99°35.39', elevation 1208 m, moist upper mixed deciduous forest (Royal Forest Department, 1962), 15 August 2009, S.C. Karunarathna (MFLU10-0065); ibid, Tambon Thasud, Muang District, Mae Fah Luang University, N 18° 05’ 59.1", E 102° 40’ 02.9", elevation 488 m, under Samanea saman (Jacq.) Merr, 17 August 2010, P. Sysouphanthong (MFLU10-0662).
Distribution: Hawaii, Israel, North America, Taiwan, China, Thailand.
Notes: Agaricus subrufescens is a rare species of the genus and the only one in section Arvenses capable to grow and fructify in tropical, subtropical and temperate climates. Its geographical distribution range extends to the Americas, Asia, Europe, and Oceania. It is a morphologically variable species. Its pileus colour varies from brown with more or less reddish hue to white. The spore size of the Chinese samples agrees with the original description (original spore size 6 4.3 mm). Agaricus subrufescens has been reported from China, but these identifications cannot be confirmed because samples were not deposited in herbaria. Agaricus subrufescens is recorded here for the first time from Guizhou Province. This species has been introduced to Asia (Japan, China) from Brazil (under the name Agaricus blazei Murrill, but in the sense of Heinemann (1993) and not in the original sense), where it is cultivated for its medicinal properties.
Fig 1. Basidiocarps of all A. subrufescens collections from northern Thailand. A: BBH19522, B-C: MFLU10-0065, D: MFLU10-0662 and E: BBH19514. Scale bars A-E = 5 cm.