Marasmius straminiceps Wannathes, Desjardin, & S. Lumyong, sp. nov.
Etymology: ‘stramineus’(L.) meaning straw coloured; ‘-ceps’ (L.) meaning head; referring to the pale yellow colour of the pileus.
Typus: Thailand: Chiang Mai Province: Doi Inthanon National Park, junction of Hwy 1009 and road to Mae Chem, N18◦ 31.58’, E98◦ 29.64’, 1703 m, sparsus vel gregarius ad folia putrida plantarum dicotyledonearum, 28 Jul. 2004, N. Wannathes 244 (CMU holotypus; SFSU- isotypus).
Pileus 2–4 mm diam, hemispherical to convex, subumbilicate to depressed, with or without a papilla, striate; surface dull, dry, glabrous, light yellow (4A4) to yellowish white (3A2) with a reddish-brown central spot. Context thin, yellowish white (3A2). Lamellae adnate to a collarium, distant (9–10) with no lamellulae, non-intervenose, narrow, cream, non-marginate. Stipe 11–35 × 0.1–0.3 mm, central, cylindrical, tough, terete, glabrous, insititious, yellowish white at apex, brown to dark brown at base; rhizomorphs absent. Odour and taste not distinctive.
Basidiospores (7–)8–10(–12) × 4–5(–6.5) mm [xmr = 8.4–9.4 × 4.4–5.1 mm, xmm = 8.9 ± 0.7 × 4.8 ± 0.5 mm, Q = 1.4–2.2, Qmr = 1.8–1.9, Qmm = 1.8 ± 0.1, n ¼ 25 spores per 2 specimens], ellipsoid, smooth, hyaline, inamyloid, thin-walled. Basidia 25–30 × 6–8 mm, clavate, 4-spored. Basidioles clavate to fusoid. Cheilocystidia common, of Siccus type broom cells; main body (7–)10–18 × (4–)7–12 mm, clavate to broadly clavate, pyriform, cylindrical or irregular in outline, rarely lobed, hyaline, thin-walled; apical setulae (2–)4–6(–7) × 0.8–1.5 mm, cylindrical to conical or irregular in outline, obtuse to subacute, hyaline to pale-yellow, inamyloid, thin- to thick walled. Pleurocystidia absent. Pileipellis hymeniform, not mottled, composed of Siccus-type broom cells; main body 11–20 × 6–10 mm, cylindrical to clavate, broadly clavate or sometimes irregular in outline, rarely lobed, hyaline, thick-walled apically, thin-walled elsewhere; apical setulae (1-)3–6 (–7) × 1–2 mm, cylindrical to conical, usually wavy in outline, obtuse to subacute, pale yellow, inamyloid, thin- to thick-walled. Pileus trama and lamellar trama interwoven; hyphae (2–)3–6 mm diam, cylindrical, smooth, hyaline, inamyloid, thin-walled, non-gelatinous. Stipe tissue monomitic; cortical hyphae 3–7 mm diam, parallel, cylindrical, smooth, brown, weakly dextrinoid to dextrinoid, thin-walled, non-gelatinous; medullary hyphae (2–)4–8 mm diam, parallel, cylindrical, smooth, hyaline, weakly dextrinoid to dextrinoid, thin- to thick-walled (>1 mm). Caulocystidia absent. Clamp connections present.
Habitat: Scattered to gregarious on undetermined dicotyledonous leaves or wood. Northern Thailand.
Material examined: Thailand: Chiang Mai Province: Doi Suthep-Pui National Park, Mok Fa waterfall on Hwy 1095, N19◦ 6.581’, E98◦46.353’, alt. 1014 m, 13 Aug. 2003, N. Wannathes106 (CMU, SFSU).
Notes: Distinctive features of this new species include the following: a pale yellow (stramineus), umbilicate pileus with a reddish-brown spot; collariate, distant (9–10), non-marginate lamellae; a lack of obvious rhizomorphs; basidiospores with mean of 8.9 × 4.8 mm and Qmm = 1.8; Siccus-type broom cells on pileipellis and lamellar edges; and growth on dicotyledonous leaves. These features indicate placement in sect. Marasmius subsect. Sicciformis. Marasmius straminiceps is phenetically similar to M. conicopapillatus, but the latter species differs in forming a white to cream-buff pileus with a distinctive, rather large conical papilla, black rhizomorphs, thick-walled cheilocystidia, and narrower basidiospores with mean 10.3 × 4.3 mm and Qmm = 2.4 (Desjardin et al. 2000). The new species is macromorphologically similar to M. platyspermus, a species described from Argentina, but the latter forms Rotalis-type broom cells and belongs in subsect. Marasmius (Singer 1976).
Fig. 1 Marasmius straminiceps (N. Wannathes 244, holotype). (A) Basidiomes. (B) Basidioles. (C) Basidiospores. (D) Cheilocystidia. (E) Pileipellis. Bar: (A) 10 mm; (B–E) 10 mm
Wannathes N, Desjardin DE, Lumyong S 2007– Mating studies, new species, and new reports of Marasmius from northern Thailand. Mycological Research 111: 985-996. https://doi.org/10.1016/j.mycres.2007.06.013