Marasmius pallidoaurantiacus Wannathes, N. Suwannarach, J. Kumla & S. Lumyong, sp. nov.

Index Fungorum number: IF 840379;  MycoBank number: MB 840379; Facesoffungi number: FoF 10682; Fig. 1

Etymology –  ‘pallio’=pale, ‘aurantiacus’=orange colour, refers to the pileus colour

Holotype –  BKF10248

Pileus 1–2 mm diam., hemispherical, umbilicate, with a tiny dark brown papilla at center; dull, dry, glabrous, slightly striate; orange white (5A2) to pale orange (5A3) with darker disc. Context thin, white. Lamellae adnate to a small collarium, distant (10–11), broad (1 mm), orange white (5A2), non-marginate. Stipe 8–13×0.2 mm, cylindrical, central; glabrous, dull, dry; insititious; dark brown overall, sometime stipe arising directly from dark brown rhizomorph.

Basidiospores 7–10(–11) × 4 – 5 ( – 6 ) µm [x=8.20±1.35×4.18±0.58, Q=1.75–2.57, q=1.97±0.30, n=25] ellipsoid, fusoid, smooth, hyaline, inamyloid, thin-walled. Basidia 14–16×4–6 µm, clavate, with 4 sterigmata, thin-walled, inamyloid. Cheilocystidia abundant, of Siccus- type broom cells; main body 5–7×4–6 µm, cylindrical to clavate, hyaline, inamyloid, thin-walled; apical setulae 1–4×1 µm, cylindrical to conical, obtuse, hyaline to pale yellow, thin- to thick-walled. Pleurocystidia absent. Pileipellis hymeniform, mottled, composed of Siccus-type broom cells; main body 10–14×4–6 µm, clavate to broadly clavate, flexuose, pale yellow, inamyloid, thin- to thick-walled; apical setulae (1–) 2–6×1 µm, cylindrical, regular in outline, obtuse, brown, thick-walled. Pileus trama interwoven, inamyloid. Lamellar trama interwoven, hyphae 2–5 µm diam., cylindrical, inflated, smooth, hyaline, inamyloid, thinwalled, non-gelatinous. Stipitipellis subparallel, hyphae 2–4 µm diam., cylindrical, dark brown, smooth, inamyloid, thick-walled (up to 1 µm), non-gelatinous. Stipe trama subparallel, hyphae 2–5 µm diam., cylindrical, hyaline to pale yellow, smooth, dextrinoid, thin-walled, non-gelatinous. Caulocystidia absent. Clamp connections present in almost all tissues.

Material examined –  Thailand, Nakhon Ratchasima Provinve, Khao Yai National Park, 33 km marker on Hyw 2090, 22 Sep 2018, collectors N Wannathes, N Suwannarach J Kumla, S Lumyong, BKF10248 (holotype), NW1108 (isotype).

Habit, habitat and known distribution –  Gregarious on dicotyledonous leave, known only from Thailand.

GenBank numbers –  MZ452673 (ITS).

Notes –  Marasmius pallidoaurantiacus is characterized by a tiny, hemispherical with dark brown conical papilla at the center, slightly striate, plae orange pileus, collariate, distant lamellae, thin stipe, sometimes arising directly from the rhizomorph, ellipsoid to fusoid basidiospores with mean 8.2 ×4.2 µm, and the presence of Siccus-type broom cell cheilocytidia. This new species is morphologically similar to Marasmius pallenticeps Singer, which was originally described from Argentina. The latter differs by forming a pure white pileus, stipe usually arising directly from rhizomorphs and the presence of nodes (Desjardin and
Ovrebo 2006). Marasmius pallidoaurantiacus pilei appear pigmented like those of M. longibasidiatus J.S. Oliveira, a species recently described from Brazil. This species differs by forming bigger (1.3–4 mm diam.), sulcate pileus, longer basidia (33–42 × 7.8–10 µm) and pileipellis composed of mixed Siccus type broom cell and non-setulost cells (Oliveira 2020). Phylogenetic analyses inferred from ITS sequence data (Fig. 2) confirmed that M. pallidoaurantiacus is a distinct species from other related morphological species and other taxa within this genus.

Figure 1 –  Marasmius pallidoaurantiacus BKF10248 (holotype). a Basidiomata, b Basidiospores, c Basidium, d Checlocystidia, e Pileipellis cell. Scale bars: a=2 mm, b–e=10 μm. Photographs and drawing by N. Wannathes

Figure 2 – Phylogenetic tree derived from maximum likelihood analysis of a combined ITS gene of 65 sequences and the aligned dataset was comprised of 1116 characters including gap. The average standard deviation of the split frequencies of the BI analysis was 0.00825. Marasmius siccus KG 039 and KG 119 were used as outgroup. Numbers above branches are the bootstrap statistics percentages (left) and Bayesian posterior probabilities (right). Branches with bootstrap values ≥70% are shown at each branch and the bar represents 0.1 substitutions per nucleotide position. Hyphen (-) represents support values ≤70%/0.95. Extype strains are in black bold. The newly generated sequences are indicated in blue and bold type species