Smithiomyces asiaticus Z.W. Ge & H. Qu, sp. nov. FIGS. 3A–B, 4A–B, 5 MycoBank MB838544
Typification: CHINA. YUNNAN PROVINCE: Xishuangbanna Prefecture, Jinghong City, Dadugang,alt. 1350 m, 29 Jun 2008, Z.W. Ge 2114 (holotype HKAS 54324). GenBank: ITS = MW522981.
Diagnosis: Distinguished from other Smithiomyces species by the presence of distinct white rhizomorphs, basidiospores with higher warts, Asian distribution, and forming a distinct species-level clade supported by mul-tiple loci (ITS, 28S, rpb2, tef1).
Etymology: asiaticus (Latin), referring to the continent where this species was collected.
Description: Pileus 24–74 mm, convex to hemispherical when young, expanding to plano-convex without an umbo when mature, often with deflexed margin, white throughout; surface smooth, not plicate, dry; with minute, white, velvety-tomentose to furfuraceous veil remnants, the veil remnants often light brown (6D7) to grayish orange (5B5) as splashed by muddy soil particles; margin often appendiculate with veil remnants (fibrillose remnants of partial veil). Lamellae free, white, densely crowded, 2–6 mm broad, with 1–3 tiers of lamellulae, segmentiform; edges even or flocculose. Stipe 22–80 × 3–7 mm, central, sturdy, cylindrical, with a slightly bulbous base; surface smooth, with an apical, membranous, white ring; lower part with white velvety-tomentose to furfuraceous veil remnants; base with white velum tissue and distinct white rhizomorphs. Context white to milky in stipe and pileus, not changing color where bruised, in the pileus 2–6 mm under the disc, hollow but stuffed with white fibers in the stipe. Smell and taste farinaceous.
Basidiospores [139/5/5] (3.5–)4–6 × 2–3.5 μm (mean 5.1 ± 0.6 × 2.9 ± 0.5 μm), Q = 1.6–2.0(–2.5), Qav = 1.80 ±0.21, ovoid to elongate, surface slightly punctate-rough under light microscope (LM); rough and with isolated, irregular warts often up to 0.3 μm under SEM (FIG. 4A–B), nondextrinoid, nonamyloid, wall not metachromatic in cresyl blue. Basidia (13–)15–19 × 5– 6(–7) μm, 4-spored; sterigmata 2–3 μm long, narrowly clavate. Cheilocystidia (12–)18–30(–36) × (4.5–)5–14(–18) μm, (2–)3–6.5(–7) μm at base, clavate to spheropedunculate, hyaline. Lamellar trama subregular, hyphae cylindrical to slightly inflated, hyaline, 4–9 μm wide. Veil remnants from pileus made up of globose elements, (30–)35–55 × 22–42(–50) μm, with hyaline to yellowish walls. Clamp connections present in all tissues.
Ecology and distribution: Presumably saprotrophic, solitary to scattered on soils in broad-leaved forests dominated by Dipterocarpaceae, Fagaceae, or Myristicaceae. Known from tropical regions in southern China, Jun to Jul.
Other specimens examined: CHINA. YUNNAN PROVINCE: Xishuangbanna Prefecture, Jinghong City,Dadugang, alt. 1350 m, 29 Jun 2008, Z.W. Ge 2105 (HKAS54314); ibid., 3 Jul 2008, Z.W. Ge 2179 (HKAS 54389);ibid., 30 Jun 2014, Z.W. Ge 3557 (HKAS 84395); ibid.,100.91482°N, 22.28536°E, alt. 1115 m, 20 Jul 2020, F.F.Liu 092 (HKAS 111974). Jinghong City, Mengla County,roadside of G213, near scenic spot of Parashorea chinensis, 7 Jul 2014, X.B. Liu 392 (HKAS 87039).
Notes: Smithiomyces asiaticus is characterized by thepresence of conspicuous white rhizomorphs at the stipebase and the basidiospores with warts up to 0.3 μm under SEM. This species appears relatively common in south-western China. Phylogenetically, S. asiaticus is distinct from known species of Smithiomyces, S. dominicanus, and S. mexicanus (FIGS. 1, 2). Morphologically, the species is similar to S. mexicanus; however, the latter occurs in Florida, Mexico (type), and Costa Rica and differs by the umbonate pileus, rough basidiospores as seen under LM, and basidiospores with isolated tiny warts under SEM (Singer 1944; Horak 1968; Vellinga 1999). No mention of white rhizomoprhs was made for S. mexicanus. Smithiomyces dominicanus is similar to S. asiaticus based on the overall appearance of the basidiomes. However, S. dominicanus is distinguished from S. asiaticus by the pileus with yellow or yellow-brown tinges when mature, the basidiospores with smaller warts under SEM, as well as a Central American distribution (Justo et al. 2015). Smithiomyces lanosofarinosus, known from Brazil, differs from S. asiaticus by the white pileus with dark red tints, sulfur yellow lamellae, and warty spores under LM (Rick 1939; Raithelhuber 1988). The sulfur yellow lamellae and dark-reddish-tinted pileus render this species aberrant from all other known species within Smithiomyces. Thus, further morphological and molecular phylogenetic studies based on recent collections from the type locality are needed in order to determine whether this species is indeed a member of Smithiomyces. Smithiomyces heterosporus, a new species described below, differs from S. asiaticus by the shorter warts (up to 0.15 μm) on the smaller basidiospores, often 2- or 4-spored basidia, and longer sterigmata up to (2–)3–5.9 μm. Smithiomyces lepiotoides, also described below from the same region, differs from S. asiaticus by the shorter warts (up to 0.15 μm) on the smaller basidiospores (4–5 × 2–3.5 μm) and rare white rhizomorphs.
