Heteroradulum kmetii (Bres.) Spirin & Malysheva, in Malysheva & Spirin, Fungal Biology 121(8): 711 (2017)
Basidiocarps perennial, first completely resupinate, later with well-developed caps, leathery, up to 5 cm in widest dimension and up to 2 mm thick, often fusing together; pilei projecting up to 1 cm. Pileal margin rather sharp, sometimes involute, margin of resupinate parts adnate, later partly detaching, concolourous to or slightly paler than hymenial surface; abhymenial surface pale ochraceous to grey, distinctly zonate, uneven, hispid. Hymenophore leathery, first smooth, pinkish or reddish, in older basidiocarps fading to pinkish grey and sometimes covered by irregularly arranged spines up to 1 mm long, in herbarium specimens with more or less pronounced vinaceous-brown stains and usually irregularly rimose.
Hyphal structure dimitic; hyphae with clamp connections. Subicular hyphae brownish, very thick-walled, arranged in parallel bundles, 2–4 µm in diam. Tramal skeletal hyphae brownish, distinctly thick-walled, interwoven in uppermost parts, more or less vertically oriented close to hymenial surface, densely arranged, (2.0–) 2.2–4.4 (–5.1) µm in diam. (n = 200/10), CB (+), sometimes irregularly inflated up to 6 µm, as a rule encrusted by solid grainy crystals; generative hyphae rather rare, hyaline, thin-to distinctly thick-walled, 2.5–4 µm in diam., but some inflated up to 5–6 µm. Skeleto-cystidia present as endings of tramal skeletal hyphae, especially abundant in senescent basidiocarps, ventricose orspindle-shaped to subglobose, very thick-walled, 4–20 µm in diam., sometimes proliferating with apical dendroid out-growths. Cystidia rarely present, clavate to bottle-shaped, 27–40 × 4–7.5 µm. Hyphidia abundant, covering hymenial surface, richly branched, 1–3 µm in diam. at the apex, often encrusted by brownish matter. Basidia obconical, four-celled, (27.4–) 29.2–45.2 (–45.4) × (9.7–) 9.8–14.5 (–14.7) µm (n = 97/10), with enucleate stalk up to 17 × 6 µm. Basidiospores cylindrical to broadly cylindrical, distinctly curved, (14.1–) 14.3–22.3 (–24.9) × (5.8–) 6.0–9.2 (–9.7) µm (n = 420/14), L = 18.38, W = 7.26, Q = 2.31–2.90.
Index Fungorum number: IF818029
Notes: Heteroradulum kmetii is a distinct species due to thick, perennial, effused-reflexed basidiocarps. However, its young basidiocarps are completely resupinate and thus they can be confused with H. deglubens. In this case, the microscopic study is necessary. The primary anatomical feature of H. kmetii is a dimitic structure: the whole basidiocarp contains abundant, thick-walled, irregularly inflated, brownish skeletal hyphae. In turn, H. deglubens is a monomitic species: thick-walled hyphae can be detected in subiculum only but they are clamped, evenly outlined (not inflated) and narrower than in H. kmetii. These species are also distinguishable due to a different construction of hymenium, composed by openly arranged basidia in H. deglubens and those ones embedded in a dense layer of hyphidia in H. kmetii. Basidiospores are highly variable in both species. Heteroradulum kmetii is a holarctic species reported here from Europe, Siberia, Russian Far East, and North America. Almost all specimens studied by us were collected from dry branches and logs of Populus and Salix spp. The species certainly prefers to open, dry habitats.
Figure 1. Combined phylogenetic nrITS D nrLSU topology from Maximum likelihood analysis showing main lineages within Auriculariales. The collection number (voucher or isolate) is given for each specimen. Support values (PP values in BI/BS values in ML/BS values in MP) are given above the branches. Scale bar shows expected changes per site.