Stereum tropicum S.H. He, Y.F. Cao & Y.L. Xu, 2025

Stereum tropicum S.H. He, Y.F. Cao & Y.L. Xu , sp. nov. MB 844730 View Materials . Figs 13C–F View Fig , 15 View Fig .

Etymology: The species epithet “ tropicum ” refers to the tropical distribution.

Typus: China, Hainan Province, Lingshui County, Diaoluoshan Nature Reserve , on fallen angiosperm trunk, 2 Jul. 2019, S.H. He, He 5968 (holotype BJFC 030843 About BJFC ) .

Basidiomes annual, resupinate to effused-reflexed, adnate, separable from substrate, coriaceous to soft corky, at first as small circular patches, later confluent up to 30 cm long, 5 cm wide, 1.5 mm thick at base. Reflexed parts projecting up to 2 cm, abhymenial surface reddish brown [8D(5–8)], sulcate, zonate, glabrous; margin distinct, light orange [5A(4–5)]. Hymenophore smooth, brownish orange [6C(4–5)] when juvenile, becoming light brown (5D5) when dry, not bleeding when fresh, slightly darkening in KOH, not cracked; margin thinning out, distinct and white when juvenile, becoming indistinct and concolourous with hymenophore surface with age. Context light brown, corky, up to 1 mm thick. Hyphal system monomitic. Subiculum distinct, light brown, composed of horizontally arranged hyphae, with crystal masses; hyphae simple septate, colourless to pale brown, thick-walled, smooth, rarely branched and septate, 3–7 µm diam. Subhymenium thickening, composed of hyphae and collapsed hymenial elements. Cystidia of three types: (1) Acanthocystidia numerous, clavate, with a few protuberances at tip part, colourless, slightly thick-walled, embedded or slightly projecting beyond the hymenium, with a basal simple septum, 20–40 × 3–5 µm. (2) Pseudocystidia tubular, colourless or pale brown, distinctly thick-walled except in the apex, embedded, 30–100 × 4–7 µm. (3) Acutocystidia scattered, colourless, thin-walled, smooth, unbranched. Basidia clavate, colourless, thick-walled, with 4 sterigmata and a basal simple septum, 20–30 × 4–6 µm; basidioles dominant, in shape similar to basidia, but slightly smaller. Basidiospores ovoid to ellipsoid, colourless, thin-walled, smooth, amyloid, acyanophilous, 5–7 × 3–4 µm, L = 6.1 µm, W = 3.4 µm, Q = 1.6–1.9 (n = 60/2).

Additional specimen examined: China, Hainan Province, Lingshui County, Diaoluoshan Nature Reserve , on dead angiosperm branch, 5 Jul. 2019, S.H. He, He 6050 ( BJFC 030925 About BJFC ) .

Notes: Stereum tropicum is characterized by resupinate to effused-reflexed basidiomes not bleeding after bruising, a bright yellow hymenophore when fresh, and the presence of acanthocystidia, and acutocystidia. Morphologically, S. rugosum is similar to S. tropicum by sharing resupinate to effused-reflexed tough basidiomes and presence of acanthocystidia but differs in having larger basidia (30–50 × 6–8 µm) and longer basidiospores (7–12 µm, Eriksson et al. 1984). Stereum tropicum is similar to S. rhododendri by having resupinate to effused-reflexed basidiomes, similar size of basidia and basidiospore length, but it is as a rule easy to determine by its thick and tough basidiomes and numerous tubular thick-walled pseudocystidia.