Hymenagaricus siamensis J. Kumla, W. Phonrob, N. Suwannar

Kumla, Jaturong, Suwannarach, Nakarin, Khuna, Surapong, Phonrob, Wiphawanee & Lumyong, Saisamorn, 2023, Hymenagaricus siamensis (Agaricaceae, Agaricales), a novel macrofungus from northern Thailand, Phytotaxa 585 (2), pp. 135-144 : 139-140

Hymenagaricus siamensis J. Kumla, W. Phonrob, N. Suwannar & S., Lumyong sp. nov. Figure 2

MycoBank number: MB846482

Diagnosis:—Distinguishable from other Hymenagaricus species by pseudoparenchymatous tissue of the pileus squamules, and from H. nigroviolaceus by its larger basidiospores and smaller pileipellis cells.

Etymology:—‘ siamensis ’ refers to the former name of the country “ Thailand ” where the holotype was collected.

Holotype:— THAILAND, Chiang Mai Province, Muang District, Chiang Mai University , 18°48´03´´N 98°57´20´´E, elevation 333 m, on soil, 29 April 2020, J. Kumla & N. Suwannarach, SDBR-CMUNK1508.

Gene sequences (from holotype):—OP836301 (ITS) and OP836385 (nrLSU).

Description:— Basidiomata small. Pileus 22‒32 mm in diameter, paraboloid when young, hemispherical to convex with age; surface dry, brownish grey (9D3), pinkish white (8A2) to dull red (8B3), sometimes brownish grey (8D2), covered by brownish orange, to brown (6C6 to 6E8) plate-like scales, with minute scattered squamules towards the margin. Lamellae, l = 3–4 series, 1.5–2 mm wide, free, pinkish white (7A2) when young, dull red (8B3) with age, up to 5 mm wide, close, with 1‒2 tiers of lamellulae. Stipe 22‒30 × 2.5‒3 mm, central, cylindrical with or without bulbous base, hollow; surface white (8A1) becoming brown (6E5) when bruised, covered with white fine squamules or fibrils. Annulus membranous, whitish, superior, attached to upper third of stipe. Context up to 5 mm thick at pileus center, white (8A1) becoming pastel red (10A4) when bruised. Spore print dark brown (8F7). Odor and teste not determined.

Basidiospores 6.5‒8.0 × 4.0‒5.0 μm, Q = 1.4‒1.88, Q m = 1.53 ± 0.11, ellipsoid to elongate, yellowish brown to brown, smooth, inamyloid, slightly thick-walled. Basidia 12‒20 × 7‒10 μm, clavate, hyaline, 4-spored; sterigmata up to 3 μm long. Pleurocystidia absent. Cheilocystidia abundant, 20.0‒42.0 × 9.0‒15.0 μm, varying in shape from subcylindrical to clavate, sometimes flexuose, hyaline, thin-walled. Hymenophoral trama regular to subregular, made up of hyaline, thin-walled hyphae, 4.0‒12.0 μm in diameter. Subhymenium layer composed of thin-walled, inflated, globose to subglobose cells, 6.0‒24.0 μm in diameter. Pileipellis a cutis of radially parallel, thin-walled hyphae, hyaline, 4.0‒10.0 μm wide. Squamules on pileal surface, pseudoparenchymatous tissues, subglobose to globose, thin-walled, with pale-brown to brown parietal and intracellular pigments, 4.0‒12.0 μm in diameter in chains. Caulocystidia absent. Stipitipellis made up of parallel, hyaline, thin-walled, 3.0‒7.0 μm wide hyphae. Stipititrama made up of parallel, hyaline, thin-walled, 8.0‒20.0 μm wide hyphae. Clamp connections absent in all tissues.

Ecology and distribution:—Fruiting solitary or gregarious on soil in grassland. Known only from the type locality in northern Thailand.

Additional specimens examined:— THAILAND, Chiang Mai Province, Muang District , Chiang Mai University , 18°48´1´´N 98°57´19´´E, elevation 350 m, on soil, 15 May 2022, W. Phonrob, SDBR-CMUWP038, gene sequences OP837533 (ITS) and OP836600 (nrLSU) .

Note:—The pseudoparenchymatous structure of the pileal squamules in H. siamensis was similar to those of H. nigroviolaceus Heinem. However , the smaller size of the pseudoparenchymatous cells (4‒12 μm in diameter) in H. siamensis differs from H. nigroviolaceus (12‒16 μm in diameter) ( Heinemann 1985). A phylogenetic analysis of the combined ITS and nrLSU sequences confirmed that H. siamensis formed a monophyletic clade and formed a sister taxon to the African taxon, H. ardosiaecolor . However, the shorter spores (5.8‒6.5 μm long) of H. ardosiaecolor clearly separate it from H. siamensis (7.0‒8.0 μm long) ( Heinemann 1956; Tibuhwa & Mwanga 2014). A pairwise nucleotide comparison of ITS data indicated that H. siamensis differed from H. ardosiaecolor by 1.97% (15/759 bp).

Figures

FIGURE 2. Hymenagaricus siamensis SDBR-CMUNK1508 (holotype). a. Basidiomata; b. Basidiospores; c. Basidia; d. Cheilocystidia and e. Cells of squamulose pileus. Scale bars: a = 10 mm; b, c = 5 μm; d,e = 10 μm.