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

Stereum rhododendri S.H. He, Y.F. Cao & Y.L. Xu , sp. nov. MB 844729 View Materials . Figs 13A, B View Fig , 14 View Fig .

Etymology: The species epithet “ Rhododendri ” refers to the host Rhododendron .

Typus: China, Fujian Province, Wuyishan Nature Reserve , on fallen Rhododendron branch, 17 Aug. 2016, S.H. He, He 4483 (holotype BJFC 023924 About BJFC ) .

Basidiomes annual, resupinate to slightly effused-reflexed, closely adnate, coriaceous, first as small patches, later confluent up to 17.5 cm long, 3.5 cm wide, 100 µm thick in section. Hymenophore smooth, white (5A1) to orange white (5A2) when fresh, pale orange (5A3) to greyish orange [5B(3–4)] when dry, turning reddish brown after bruised when fresh, becoming dark brown when dry, unchanged in KOH, not cracked; margin adnate or slightly elevated, distinct, paler or concolourous with hymenophore surface. Hyphal system monomitic. Subiculum distinct, pale brown, hyphae colourless to pale yellow, slightly to distinctly thick-walled, smooth, simple-septate, rarely branched and septate, more or less parallel to the substrate, 2.5–5 µm diam. Subhymenium thickening, composed of hyphae and collapsed hymenial elements. Cystidia of two types: (1) acutocystidia subfusiform, colourless, thin- to slightly thick-walled, smooth, usually with a tapered apex, embedded or rarely projecting beyond the hymenium, 15–35(–50) × 3–6 µm; (2) gloeocystida fusiform or subclavate, thin-walled, smooth, often with yellow contents, embedded, 20–60 × 3–8 µm. Basidia clavate, colourless, thin-walled, with 4 sterigmata and a basal simple septum, 20–30 × 3–6 µm; basidioles dominant, in shape similar to basidia, but slightly smaller. Basidiospores ellipsoid to subcylindrical, colourless, thin-walled, smooth, amyloid, acyanophilous, (4.2–)5–7 × 2–3 µm, L = 5.7 µm, W = 2.6 µm, Q = 2.1–2.3 (n = 60/2).

Additional specimens examined: China, Fujian Province, Wuyishan Nature Reserve , on fallen Rhododendron branch, 17 Aug. 2016, S.H. He, He 4459 ( BJFC 023900 About BJFC ); ibid., He 4481 ( BJFC023922 About BJFC ) .

Notes: Stereum rhododendri is characterized by resupinate to slightly effused-reflexed basidiomes, presence of acutocystidia and gloeocystidia, absence of thick-walled cystidia, relatively small basidiospores and host of Rhododendron . In the phylogenetic tree ( Fig. 1 View Fig ), S. rhododendri formed a distinct lineage sister to S. rugosum and S. sanguinolentum . Morphologically, S. rugosum can be easily separated from S. rhododendri by having dimitic hyphal system, thick-walled pseudocystidia, and lager basidiospores ( Chamuris 1988). Stereum sanguinolentum is similar to S. rhododendri by sharing resupinate to effused-reflexed basidiomes with hymenophore darkening when bruised, but differs in having acanthocystidia, thick-walled gloeocystidia, and slightly larger basidiospores (7–10 × 3–4.5 µm), and growing on Pinus trees ( Eriksson et al. 1984).