Aleurodiscus isabellinus S.H. He & Y.C. Dai

Tian, Yan, Ghobad-Nejhad, Masoomeh, He, Shuang-Hui & Dai, Yu-Cheng, 2018, Three new species of Aleurodiscus s. l. (Russulales, Basidiomycota) from southern China, MycoKeys 37, pp. 93-107 : 97-99

Aleurodiscus isabellinus S.H. He & Y.C. Dai sp. nov. Figs 2c, 4

Diagnosis.

The species is distinct by having soft, yellow to yellowish-brown and corticioid basidiomata, a loose texture, abundant yellow acanthophyses, simple-septate generative hyphae and smooth basidiospores 6-8.5 × 3-4 μm.

Holotype.

CHINA. Yunnan Province, Dali County, Cangshan Nature Reserve, alt. ca. 2600 m, on fallen decorticated angiosperm branches, 27 Oct 2017, KKN-2017-19 (holotype in CFMR, isotype in BJFC).

Etymology.

“Isabellinus” refers to the yellowish-brown basidiomata.

Basidiomata.

Annual, resupinate, effused, adnate, inseparable from substrate, soft, membranaceous to coriaceous, at first as small patches, later confluent up to 15 cm long and 1 cm wide, 150-300 μm thick. Hymenophore smooth, light orange [5A(4-5)], greyish-orange[5B(5-6)], orange [5B(7-8)] to brownish-yellow [5C(7-8)], uncracked or cracked with age; margin thinning out, fimbriate, white (5A1) when juvenile, becoming abrupt, indistinct, concolorous with hymenophore when mature.

Microscopic structures.

Hyphal system monomitic, generative hyphae simple-septate, colourless, thin- to slightly thick-walled, straight, loosely interwoven, frequently branched and septate, 2-4 μm in diam. Acanthophyses abundant, colourless to yellow, thick-walled, hyphoid or arising laterally or apically from a clavate or cylindrical base 30-50 × 5-7 μm, with abundant spines in upper part, some hyphoid ones near substrate with long spines (branches) resembling binding hyphae. Gloeocystidia abundant, embedded, colourless, slightly thick-walled, subcylindrical or slightly moniliform, negative in sulphobenzaldehyde, 35-110 × 5-8 μm. Basidia clavate, colourless, thin-walled, with four sterigmata and a basal simple septum, 40-55 × 6-7 μm. Basidiospores ellipsoid to oblong ellipsoid, bearing a distinct apiculus, colourless, thin-walled, smooth, amyloid, (5.5-) 6-8.5 × (2.8-) 3-4 μm, L = 7 μm, W =3.7 μm, Q = 1.9 (n = 24/1).

Additional specimens examined.

CHINA. Yunnan Province, Dali County, Cangshan Nature Reserve, alt. ca. 2600 m, on small dead bamboo, 27 Oct 2017, He 5283 (BJFC 024801) and He 5287 (BJFC 024805); on fallen angiosperm branch, 27 Oct 2017, He 5294 (BJFC 024812); Jingdong County, Ailaoshan Nature Reserve, alt. 2450 m, on fallen angiosperm branch, 4 Oct 2017, C.L. Zhao 3843 (SWFC).

Remarks.

All the studied specimens of A. isabellinus lack a true hymenium and only the holotype has a few basidia and basidiospores. Aleurodiscus isabellinus was nest ed within the A. cerussatus group (Fig. 1). In this group, Aleurodiscus thailandicus S.H. He is similar to A. isabellinus by sharing the yellow basidiomata and acanthophyses, but differs by having two types of gloeocystida and acanthophyses without a clavate or cylindrical base ( Dai et al. 2017a). The ITS similarity between A. isabellinus (He 5283) and A. thailandicus (He 4099) is 93.6% of 578 base pairs. Aleurodiscus thailandicus was described from Thailand based on a fertile specimen on bamboo, but later several sterile specimens on bamboo from south-western China were identified as this species according to the sequence data. Morphologically, the soft and yellow to yellowish-brown basidiomata of A. isabellinus resemble the genus Vararia P. Karst. which belongs to Peniophoraceae according to phylogenetic analyses.