Pseudohydnum purum L. Lei & Q. Zhao, 2025

Lei, Lei, Luangharn, Thatsanee, Yu, Feng-Ming & Zhao, Qi, 2025, Two new species of Pseudohydnum (Auriculariales, Basidiomycota) from the Qinghai-Tibet Plateau in China, Phytotaxa 690 (2), pp. 243-254 : 248-250

Pseudohydnum purum L. Lei & Q. Zhao , sp. nov. ( Figs. 2 , 4 )

Index Fungorum number: IF903031; Facesoffungi number: FoF 16968

Etymology:—The epithet “purum ” refers to the pure white basidiomata.

Diagnosis:— Pseudohydnum purum is similar to P. viridimontanum small-sized and whitish basidiomata, but can be distinguished from P. purum by its smaller basidiospores and presence of cylindrical to fusiform inflated elements in the spine tramal hyphae.

Holotype:— CHINA, Xizang, Rikaze, Dingjie , 27.91598793°N, 87.36751710°E, alt. 2,933 m, 04 Jul. 2022, coll. Lei Lei, LEI-426 ( KUN-HKAS 134352 ).

Basidiomata small-sized, tapering upwards when young. Pileus 10–20 mm diam, gradually unfolds after maturity, irregular sucker-like; surface velutinous or mastoid, white when fresh and pale olive-brown (4D4) or light brown (5D4) when dried, gelatinous when fresh, brittle when dried. Spines when dried up to 0.5 mm long and 6−10 per mm at the base, conical, white when fresh, and pastel yellow (2D5) to buff olive (2 A 4) when dried. Context 1–2 mm thick, translucent, unchanging colour when injured, resilient. Stipe 15–25 × 8–13 mm, lateral, flat-cylindrical to cylindrical, gelatinous, translucent, velutinate, surface concolourous with pileus surface.

Basidiospores: (6.5–) 7.0–8.5 (–9.0) × (5.5–) 6.0–7.5 (–8.0) μm, L m = 7.5 μm, W m = 6.7 μm, Q = 1.07–1.19 (n = 60/3/2), Q m = 1.13 ± 0.06, broadly ellipsoid to subglobose, hyaline, thin-walled, with a big guttule. Probasidia 11.8−16.4 × 8.9−13.3 μm, fusiform to lageniform. Hyphidia 1.5−3 μm wide, occasionally branched. Basidia 9.6−14.9 × 11.0−14.4 μm, four-celled, barrel-shaped, globose to subglobose, with guttules, sterigmata up to 17 × 1.4−3.3 μm. Contextual hyphae 1.5−5.5 μm wide, frequently branched, interwoven, thin- to slightly thick-walled, hyaline. Tramal hyphae 1.5−4.0 μm wide, frequently branched, interwoven, thin-walled, hyaline. Pileipellis is composed of subparallel or ascending hyphae, 2.0–4.5 μm wide, interwoven, thin- or slightly thick-walled, hyaline. Clamps are common in all parts of basidiomata.

Habitat:—Solitary or gregarious, growing on rotten wood in theropencedrymion, mainly include: Pinus , Rhododendron , Sorbus , Taxus , Toxicodendron , and Viburnum .

Additional material examined:— CHINA, Xizang, Rikaze, Dingjie, 27.91598793°N, 87.36751710°E, alt. 2,933 m, 04 Jul. 2022, coll. Feng-Ming Yu, FM 22-425 ( KUN-HKAS 134353).

Notes:— Pseudohydnum purum is characterized by small-sized basidiomata, irregular and sucker-like pileus with a white surface, flat-cylindrical white stipe, and broadly ellipsoid to subglobose basidiospores. Morphologically, P. purum resembles P. cystidiatum , P. translucens , and P. viridimontanum on the small-sized and whitish basidiomata. However, P. purum differs from P. cystidiatum in that the latter has a very short or absent stipe and the presence of cystidia ( Spirin et al. 2023). Pseudohydnum viridimontanum can be distinguished from P. purum by its smaller basidiospores (5.6–6.9 × 4.3–5.0), and the presence of cylindrical to fusiform inflated elements in the spine tramal hyphae ( Coelho-Nascimento et al. 2024). In contrast to P. purum , P. translucens (5.4–7.4 × 4.2–6.9 μm) has smaller spores ( Zhou et al. 2023). In the LSU + ITS phylogenetic tree ( Fig. 1 ), P. purum forms a well-supported clade ( MLBP = 100, BIPP = 1.00) and is grouped as a sister clade to P. viridimontanum with a more substantial support value ( MLPP = 100, BIPP = 1.00), and occupied a basal position within the genus Pseudohydnum .

Figures

FIGURE 1. Maximum likelihood tree based on the combined LSU and ITS dataset, showing the phylogenetic position of Pseudohydnum spp. Bootstrap proportions (MLBP) equal to or above 70%, and equal to or above 0.90 proportions (BIPP) are shown above the branches of the phylogenetic tree. The newly generated sequences and type specimens are shown in red or bold, respectively.

FIGURE 2. Basidiomata of Pseudohydnum. a−c P. motuoense (a. KUN-HKAS 134349; b KUN-HKAS 134347, holotype; c KUN-HKAS 134348); d−f P. purum (d KUN-HKAS 134352, holotype; e, f KUN-HKAS 134353). Bars: = 1 cm.

FIGURE 4. Microscopic features of Pseudohydnum purum (KUN-HKAS 134352 holotype). a basidiospores, showing germination by repetition; b basidia, hyphidia; c hyphae of pileus surface. Bars: a−b = 10 μm; c = 20 μm.