Hohenbuehelia tristis

Hohenbuehelia tristis G. Stev.

MycoBank No: 332010

Pileus 15–20 × 20–30 mm, spathuliform to reniform, dimidiate to orbicular, greyish-white (1B1) to yellowish white (1B2) when young, becoming white (1A1) in age, glutinous, very faintly translucent, shiny when mature; upper surface minutely pubescent with grayish hairs (5A1–5B1) near the point of attachment and more sparsely so towards the margin as observed with a lens, with hairs disappearing when old; margin incurved becoming upturned in age. Lamellae radiating from point of attachment, 1 mm broad, very crowded, white (1A1) to pale yellow (1A3); lamellulae in (1)–4 tiers. Stipe absent, or pseudostipe sometimes present, laterally or dorsally attached, 1 mm long when young then disappearing when old. Context consisting of two layers: 1) leathery layer, 1 mm thick; 2) gelatinous layer, 1–2 mm thick, soft, sticky, colorless. Order and Test not observed. Spore print white. Basidiospores [150/3/2] (5.1–)6–6.8–8(–9) × (3.5–)3.5–4.0–5(–5.2), Q = (1.21–)1.38–1.70–2.08(–2.26), ellipsoid, sub-ellipsoid to elongate, smooth, thin-walled, inamyloid. Basidia (13–)14–21.2–24(–24.2) × (5–)5.5–6.6– 7(–7) µm, clavate to subcylindrical, mostly with 4 sometimes with 2 sterigmata, 2–4 µm long, hyaline, smooth, thin-walled. Cheilocystidia (10.9–)11–13.1–19(–19.8) × (4.2–)4.4–5.5–6.5(–6.5) µm, lecythiform to sublageniform, subcapitate to capitate apex, hyaline, thin-walled. Pleurocystidia (38–)38–61.5–82(–82) × (10.7–) 11–15.0–18.5(–18.6) µm, subfusiform, narrowly fusiform to fusiform, brownish, encrusted with crystals when observed in water, but crystals disappearing in KOH. Hymenophoral trama subregular, hyphae 2–4 µm wide. Pileipellis as tufts of ixotrichoderm with cylindrical terminal elements 40–105 × 3–5.5 µm, with light brown intracellular pigments. Pileoleptocystidia absent. Pileus trama consisting of two layers: 1) upper layer gelatinous, composed horizontally arranged, smooth, colorless, encrusted hyphae, 1.5–2.5 µm wide; 2) lower layer non-gelatinous, composed interwoven, smooth and hyaline hyphae, with2–4 µm. Clamp connections present in pileipellis, pileus trama, and hymenophoral trama.

Habitat. Solitary, gregarious to imbricate, on dead small branches.

Additional specimens examined. THAILAND. Chiang Rai Province, Muang Chiang Rai District, Nang Lae Nai village, 31 July 2019, Monthien Phonemany (MFLU22-0015).

Notes: Two accessions identified as H. grisea, the culture MFLUCC 12-0451 from Thailand and HFJAU0029 from China (unpublished), had the same ITS sequence than H. tristis (MFLU22-0015 and MFLU22-0016) except for three substitution heteromorphisms in the ITS sequence of MFLU22-0016. The two former sequences retrieved from GenBank have no corresponding morphological descriptions available as evidence. Therefore, these might have been wrongly identified, since ITS sequences are identical to sequences obtained from our collections of H. tristis. Additional confirmation of the taxonomic identity of our specimens was obtained by comparing the morphology of our specimens with H. grisea which was originally described as Pleurotus atrocoeruleus var. griseus Peck from New York. The latter is distinguished by a greyish to greyish-brown, sparsely tomentose pileus, the lamellae becoming cream-coloured in age (Peck 1891). Hohenbuehelia tristis is characterised by reniform basidiomata, minutely pubescent pileus with greyish hairs that disappear when mature, leaving the surface gelatinous, faintly translucent and shiny, ellipsoid to sub-ellipsoid basidiospores, lecythiform to sublageniform cheilocystidia, and an ixotrichoderm pileipellis. Hohenbuehelia tristis described from New Zealand differs from our collections (MFLU2022-0015 and MFLU2022-0016) by having smaller basidiomata (10–20 × 10–15 mm), smaller (mostly narrower) basidiospores (7 × 3 μm), larger and pseudo-amyloid metuloids (80–90 × 15–20 μm), pileipellis as tufts of parallel larger hyphae (3–8 μm in diam.) (Stevenson 1964). In our phylogenetic analysis (Fig. 1), the Thai accessions of H. tristis formed a monophyletic group with the accessions of H. tristis from New Zealand. The morphological differences we observed between the Thai and New Zealand accessions suggested that they might not be conspecific. Additionally, the single synapomorphic position we observed in the LSU sequence is not incompatible with two distinct species, since a genetic distance of only one substitution can be observed between other closely-related species (e.g. H. tremula and H. longipes; Table 4). However, the LSU sequence of the Thai specimen MFLU22-0016 showed two to three heteromorphisms corresponding to the differences between the other Thai specimens and the New Zealand specimens. This suggests either incomplete lineage sorting or that the two lineages can still interbreed. Heteromorphisms were also observed in the ITS sequence of MFLU22-0016, but we could not compare with ITS sequences of materials from New Zealand, which were unavailable. In view of all the heteromorphisms, we decided not to treat the Thai materials as a new species distinct from H. tristis.

Fig. 1 Phylogeny of selected sequences of Hohenbuehelia based on a maximum likelihood analysis of three nuclear gene regions (nrITS, nrLSU, tef1). The Maximum likelihood bootstrap values (BS ≥ 70%) and Bayesian posterior probabilities values (PP ≥ 0.90) are shown on the branches. Newly sequenced collections are in bold. Five Pleurotus species were used as outgroup. (T) designates holotypes. The sequence H. flabelliformis voucher number MFLU22-0008 was identical to MFLU22-0009 (ITS only). Sequences of H. lageniformis voucher number MFLU22-0010 were identical to MFLU22-0012 (ITS and LSU). Sequences of H. tristis subsp. macrocarpa voucher number MFLU22-0016 were identical to MFLU22-0015 (ITS and LSU) and to the two specimens MFLUCC 12-0451 and HFJAU0029 identified as H. grisea (both only ITS) from GenBank, except for three substitution heteromorphisms in the ITS sequence of MFLU22-0016.