Dendrogloeon helenae Spirin, Ryvarden & Miettinen. , in Spirin et al., Synopsis Fungorum (Oslo) 33: 26 (2015)
Basidiocarps resupinate, grayish white, tough ceraceous, 0.03–0.05 mm thick, margin indistinct. Hymenial surface smooth, margin not differentiated. Hyphal structure monomitic, hyphae clamped. Subicular hyphae very densely arranged and partly glued together, slightly thick-walled, faintly cyanophilous, 3–4 μm in diam. Basidiospores broadly ellipsoid to subglobose, thin-walled, (8.1–) 8.3–10.3 (–10.4) × (6.2–) 6.5–8.3 (–9.2) μm, L = 9.23, W = 7.53, Q’ = (1.1–) 1.2–1.4 (–1.5), Q = 1.23 (n = 20/1), with large central oil drop, inamyloid, acyanophilous. Basidia obovate, four-celled, (18.3–) 18.4–26.2 (–26.9) × (9.7–) 9.8–12.7 (–13.0) μm, slightly thick-walled (wall 0.3–0.5 μm thick), guttulate, with rather thick and straight, mostly blunt sterigmata up to 11 × 5 μm. Tramal / subhymenial hyphae densely arranged, thin-walled, 2–3 μm in diam. Gloeocystidia abundant, narrowly clavate, 22–28 × 5–8 μm (n = 10/1), with brownish, strongly cyanophilous content. Dendrohyphidia abundant, richly dichotomously branched, 1–2.5 μm in diam., embedded or slightly projecting, in some parts apically encrusted by rosette-like or stellate crystals.
D. helenae is so far known only from the type locality. Both nLSU and ITS sequences of the species give no close matches in GenBank. D. helenae is undoubtedly a member of the Auriculariales but it is very distant from other genera possessing similar morphological characters. The presence of gloeocystidia and almost subglobose spores brings Basidiodendron to mind, but species of the latter genus have thin-walled, shorter, broadly urniform or subglobose basidia, which collapse and form involucre-like structures in older basidiocarps (Luck-Allen 1963, Wells & Raitviir 1975). The sole representative of Bourdotia, B. galzinii, has stalked (petiolate) basidia and a well-developed epihymeniallayer consisting of densely arranged hyphidia (Wells & Raitviir 1975, Weiss & Oberwinkler 2001). No gloeocystidiate species are known in Exidiopsis; however, the latter genus is highly artificial in morphological terms and certainly polyphyletic.
Figure 1. Dendrogloeon helenae (from the holotype): hymenial cells and basidiospores. Scale bar = 10 μm.
Spirin V, Ryvarden L, Miettinen O. 2015. Notes on heterobasidiomycetes from St. Helena. Synopsis Fungorum. 25–31.