Collybiopsis gibbosa (Corner) R.H. Petersen, in Petersen & Hughes, Mycotaxon 136(2): 342 (2021)

Index Fungorum number: IF 556187; Mycobank number: MB 556187; Facesoffungi number: FoF 16480; Fig. 1

Basionym – Marasmius gibbosus Corner. 1996. Nova Hedwigia, Beih. 111: 53.
= Marasmiellus gibbosus (Corner) J.S. Oliveira. 2019. Mycol. Prog. 18: 734.
= Gymnopus gibbosus (Corner) A.W. Wilson, Desjardin & E. Horak, Sydowia 56: 175. 2004.

Basidiocarps medium-sized, Pileus 7.0‒33.4 mm in diam, convex when young, becoming undulating with age; margin inflexed or slightly reflexed, striated; surface smooth, hygrophanous, center light brown (6D6) to gray, orange (6B5), orange, white (6A2) to whitish (6A1) at margin. Lamellae subdistant, adnexed, white (1A1), margin even. Stipe 26.4‒55.6×2.8‒5.8 mm, central, cylindrical, glabrous, tapered toward apex, swollen to the side at base, whitish (1A1) to greyish yellow (4B4). Basidiospores 4.5‒8.3×2.8‒6.0 μm, average 6.00×4.06 μm, Q=1.0‒2.1 (mean=1.49), subglobose to obovoid to lacrymoid, smooth, thin-walled, with drops. Basidia 14.7‒24.8×3.7‒6.8 μm, 4-spored, clavate to narrowly clavate. Pleurocystidia absent. Cheilocystidia 30.5‒128.1×5.7‒13.3 μm, narrowly cylindrical, subinflated, thin-walled, smooth, branched. Caulocystidia 16.1‒50.3×3.2‒6.0 μm, narrowly cylindrical to flexuose, irregular. Pileipellis hyphae 3.6‒8.3 μm wide, thick-walled, intricate trichoderm. Stipitipellis hyphae 3.1‒7.2 μm, curved trichoderm. Clamp connection present in all tissues. Odour and taste not recorded.

Habitat: Gregarious in soil covered with leaf litter under Samanea saman.

Materials examined – Thailand, Chiang Rai, Muang District, Mae Fah Luang University, 20° 03′ 14″ N, 99° 53′ 37″ E, alt. 413 m, 11 August 2020, Yuwei Hu, HYW117 (MFLU 24-0038). Chiang Rai, Muang District, Mae Fah Luang University, 20° 03′ 17″ N, 99° 53′ 43″ E, alt. 411 m, 13 August 2020, Yuwei Hu, HYW127(MFLU 24-0039).

GenBank numbers – ITS: OR815366 (MFLU24-0038), OR815367 (MFLU24-0039), LSU: OR815384 (MFLU24-0038),OR815385 (MFLU 24-0039)

Notes – This species was first described from Singapore, Java, and Republic of São Tomé and Príncipe as Gymnopus gibbosus (Corner 1996; Wilson et al. 2004; Desjardin & Perry 2017). The collections from this study are morphologically similar to Gymnopus gibbosus. Thai collections of Collybiopsis gibbosa has moderately-sized basidiocarps; light brown disc and whitish margin; white lamellae; grayish yellow stipe (brown stipe for Gymnopus gibbosus); basidiospore mean 6.00×4.06 μm (8.5×4.7 for Gymnopus gibbosus); cylindrical cystidia; pileipellis and stipitipellis hyphae intricate trichoderm (cutis-type for Gymnopus gibosus). Based on Petersen & Hughes (2021), Gymnopus gibbosus is synonymous with Collybiopsis gibbosa. In ITS sequence phylogenetic analysis, HYW117 and HYW127 showed 100% similarity to Brazil collections of URM90006 and URM90012, and 99.72% to Australian collection MEL: 2382838. In combined ITS-nrLSU phylogenetic analysis, Collybiopsis gibbosa is sister to Collybiopsis luxurians and Collybiopsis pseudoluxurians clade with 80% BS and 1.0 PP support (Fig. 2). The collections of this study represent a new geographical record of Thailand.

Figure 1 – Collybiopsis gibbosa (HYW117, new geographical record). a, basidiocarps in natural environment, b, basidiocarps in laboratory, c–e, basidiospores, f, basidia, g, basidioles, h cheilocystidia, i, caulocystidia. Scale bar: b=5 cm, c–e=3 μm, f–g=10 μm, h–i=20 μm

Figure 2 – Phylogenetic tree generated by ML analysis based on combined ITS and LSU sequence data of Gymnopus, Collybiopsis and its closely related taxa. The analyses included 121 strains and the 599 tree is rooted with Omphalotus olearious (CBS102282), Omphalotus japonicus (CBS374.51), Omphalotus ovilascens (TENN56257), and Omphalotus flagelliformis (HKAS 76645). The tree topology of the ML analysis was similar to the BYPP. The best-scoring RAxML tree with a final likelihood value of − 20,386.607306 is presented. The matrix had 787 distinct alignment patterns, with 21.27% of undetermined characters or gaps. Estimated base frequencies were as follows: A=0.246718, C=0.181088, G=0.257374, T=0.314820; substitution rates AC=0.796329, AG=5.315752, AT=1.623571, CG=0.450011, CT=5.454699, GT=1.000000; gamma distribution shape parameter α=0.256828. RAxML bootstrap support≥50% and Bayesian posterior probabilities≥0.50 (BYPP) are indicated above the nodes. The scale bar indicates 0.04 changes per site. New sequences recovered in this study are in bold black