Xanthagaricus minimus Kun L. Yang, Jia Y. Lin, Zhen-Chao Liu & Zhu L. Yang

Yang, Kun L., Lin, Jia Y., Li, Guang-Mei, Liu, Zhen-Chao, Hosen, Md. Iqbal & Yang, Zhu L., 2024, Heinemannomyces, Hymenagaricus and Xanthagaricus revisited (Basidiomycota, Agaricaceae), Phytotaxa 659 (2), pp. 112-164 : 138-139

Xanthagaricus minimus Kun L. Yang, Jia Y. Lin, Zhen-Chao Liu & Zhu L. Yang , sp. nov. ( Fig. 10 )

Registration identifier:— FN571942

Etymology:— Referring to the tiny basidiomata of this species.

Diagnosis:— Differing from other Xanthagaricus species by a tiny pileus not exceeding 3 mm in diameter when mature.

Type:— China, Guangdong Province, Guangzhou City, Huangpu District, Jiangdong Village , Boluoshan Hill , on soil, 23°11’31”N, 113°32’48”E, elevation 150 m, August 27, 2023, Zhen-Chao Liu, Kun L. Yang & Jia Y. Lin, S 23542 ( HKAS133465 (ITS: PP736744; nrLSU: PP732974 )) .

Description:— Basidiomata tiny. Pileus 0.5–3 mm in diameter, hemispherical to plano-convex; background merino white (#F9F5EC); squamules granular to furfurous, milky yellow (#FFF07A), lion orange (#EFD871) to sandy orange (#E6CF73), becoming lighter towards margin; margin with appendices concolorous with or lighter than the squamules on the pileus; context ceramic white (#FEFEFA) to merino white (#F9F5EC) when fresh, without a color change or becoming darker after damaged. Lamellae free, subdistant, merino white (#F9F5EC) to cherrywood brown (#DAB697), with a slightly serrate edge; lamellulae abundant. Stipe 3–8 mm long, 0.5 mm thick, subcylindrical, tapering downwards, slightly curved; background medium gray (#E0DEDD), dull thatch yellow (#D3D3B7) to dull silver gray (#A7A6A5); squamules furfurous, usually more abundant below the annulus, merino white (#F9F5EC) to medium gray (#E0DEDD); context ceramic white (#FEFEFA) to merino white (#F9F5EC) when fresh, without a color change or becoming darker after damaged; base without tomenta. Annulus superior, easily broken and fugacious, concolorous with the squamules on the stipe. Odor unknown. Taste unknown.

Basidiospores [40/2/2] 4–5.5 [4.70 ± 0.40, 4.50] × 2.5–3 [2.88 ± 0.22, 3.00] µm, Q = 1.50–1.83 (2.00) [1.64 ± 0.14, 1.50], ellipsoid to oblong, slightly thick-walled, smooth under LM, sparsely verrucose under SEM, tinged moon yellow (#FAF9AA) to mana yellow (#F7F57E) in both water and 5% KOH, with a small apiculus, without a germ pore. Basidia 12–15 × 4.5–6 μm, clavate, 4-spored, thin-walled, nearly colorless in both water and 5% KOH, with sterigmata up to 2.5 µm long, surrounding by basidioles measured 6–14 × 4–5.5 μm. Lamella trama regular to subregular, composed of 3–5 µm wide, cylindrical to subcylindrical, thin-walled, nearly colorless in both water and 5% KOH, compact, moderately to frequently branching hyphae. Cheilocystidia abundant, 8–16 × 4.5–6.5 µm, broadly clavate to clavate, thin-walled, smooth, nearly colorless in both water and 5% KOH. Pleurocystidia absent. Pileus squamules epithelioid to subhymeniform, composed of slightly thick-walled and encrusted, ellipsoid to to clavate terminal cells measured 11–20 × 5.5–11 µm, on globose to subglobose cells measured 5.5–26 × 4–17, tinged butter orange (#F2DF8F) in both water and 5% KOH. Stipe squamules intricate trichoid, composed of 2.5–5 µm wide, cylindrical to subcylindrical, thin- to slightly thick-walled and encrusted hyphae, tinged butter orange (#F2DF8F) in both water and 5% KOH. Clamp connections absent in all tissues.

Habitat and distribution:— Solitary to gregarious, scattered on soil as individuals, in southern subtropical monsoon forests. Currently known from China (South China).

Additional collections examined:— China, Guangdong Province, Guangzhou City, Huangpu District, Jiangdong Village , Boluoshan Hill , on soil, 23°11’31”N, 113°32’48”E, elevation 150 m, August 28, 2023, Zhen-Chao Liu, Kun L. Yang & Jia Y. Lin, S 23568 ( HTBM1679 (ITS: PP736749; nrLSU: PP732979 )) ; same location, April 16, 2024, Zhen-Chao Liu, Kun L. Yang & Jia Y. Lin, S 24011 ( HTBM1977 ) & S24012 ( HTBM1978 ) .

Figures

FIGURE 10. Xanthagaricus minimus (Photos by Zhen-Chao Liu, Kun L. Yang & Jia Y. Lin; drawings by Kun L. Yang & Jia Y. Lin, from HKAS133465 (holotype), HTBM1679 & HTBM1978). a–d. Basidiomata (a. HTBM1977; b. HKAS133465 (holotype); c. HTBM1679; d. HTBM1978). e–g. Basidiospores (e–f. SEM photos of HTBM1679 in multi-angle views; g. Line drawing). h. Cheilocystidia. i. Hymenium and subhymenium. j. Squamules at pileus center. k. Stipe squamules. Bars: b–d = 2 mm, e–f = 2 µm, g–i = 5 µm, j = 20 µm, k = 10 µm.