Tricholomopsis lechatii Courtec., S. Dumez, S. Welti & P.-A. Moreau, sp. nov.
Index Fungorum number: IF 843163; MycoBank number: MB 843163; Facesoffungi number: FoF 13397; Fig. 1
Etymology – The species is warmly dedicated to our friend Christian Lechat (1952–2022), who recently and suddenly died. He was an eminent specialist of the Hypocreales worldwide and a very enthusiastic and faithful member of the numerous field trips organized in the Tropics by one of us (RC). He was present when this species was collected.
Holotypus – 0202264 (LIP).
Pileus 10–14 mm diam, slightly convex or almost flat, showing a little umbilic (not deep) in the centre or slightly eccentric; shape regular, circular or almost so, sometimes slightly elliptical when seen from above. Surface remarkably dull, finely tomentose or even velvety under lens. Color very special, dirty olivaceous with ochraceous hue at center but more yellow at the margin, which is slightly enrolled or at least very obtuse and scarcely pectinate at the extreme edge. Lamellae adnate, rather crowded, with two rather regular rows of smaller gills, thin. Color rather bright and deep, mustard yellow. Edge rather thick, clearly bearing a row of small, densely crowded, aggregates of crystals. Stipe up to 15×2 mm, slightly excentrical, cylindraceous, more or less narrowly fistulose, dull yellow, paler than the gills but sometimes pale brownish toward mid-length, arising from a thin greyish mycelial patch of subiculum (up to 35 mm diam.), which sometimes climbs up to the stipe up to a few millimeters, thus greyish at the basis. Context yellowish in the stipe, deeper yellow in the cap. Smell none. Taste not recorded.
Basidiospores 6.2–7.5×4.8–5 µm, rather broad, elliptical to slightly tear-shaped, apex broader and generally clearly rounded (not elongate nor conical). Apiculus small, faintly distinct. Content with many droplets (sometimes a large one) and confuse, cloudy or punctate around them. Wall smooth, inamyloid, not cyanophilic. Basidia 20–28 × 5–8 µm, 2-spored (very few 1-spored and only one 3-spored seen) with very long and sharp sterigmata (up to 10 µm), containing large droplets, the bigger ones at the top. Clamp present at the base of all basidia. Subhymenium ramose, rather thick with short, clamped hyphae up to 1.5–2.5 µm wide, somewhat wavy with some longer hyphae parallel to the hymenium. Hymenophoral trama parallel in a wavy arrangement, weakly interwoven, made of clamped hyphae 4–8 µm wide. Edge sterile; cheilocystidia very numerous and prominent, cylindrical to slightly clavate, often regularly thickened toward apex, 35–45×8–12 µm, thin-walled, hyaline; base clamped, originated from simple or rarely forked hyphae. Pleurocystidia absent; facial sterile cells present as sparse slender “hyphids” cylindrical or slightly thickened at apex, up to 4 µm wide. Pileipellis a trichoderm of more or less straightly erected, unicellular or sometimes articulate elements, rather densely arranged, 30–70×7–15 µm, the apex mostly rounded or sometimes irregular, rarely mucronate to appendiculate or exceptionally forked; pigmentation epiparietal and vacuolar: wall yellowish, very finely incrusting (minutely punctate or finely marked with transverse zebra depending on the focus made on the cell wall) in all parts of the basidiome; vacuolar pigment abundant in subpellis, also present in broad elements of suprapellis, brown-yellow.
Habitat – Saprobic on rotten wood of unidentified Angiosperm, wet tropical forest, along a wet depression. So far only known from the type locality, French Guiana.
Material examined – French Guiana: Saül, Roche Bateau trail, 23 Aug. 2018, R. Courtecuisse & C. Lechat, RC/Guy18.018 (LIP 0202264, holotype).
GenBank numbers – LIP 0202264-OM793061 (ITS), OM793062 (LSU).
Notes – Tricholomopsis lechatii phylogenetically belongs to the T. aurea-complex, a pantropical group of collybioid species so far rather poorly documented in molecular databases (Fig. 2). Tricholomopsis aurea was originally described from DR Congo (as Marasmius aureus; Beeli, 1928), and recently transferred in the genus Tricholomopsis by Desjardin and Perry (2017) based on recent collections from São Tomé. Although the species is reported as common in many tropical regions (GBIF data: https://www.gbif.org/en/species/332554), only few sequences from the neotropics are available, and the ITS marker indicates only faint differences between African and American collections (Desjardin and Perry 2017, consider them as conspecific at this time). The new species described here differs significantly from T. aurea, by a pileipellis of trichodermioid structure, with a well-differentiated subpellis and a distinct vacuolar pigment (responsible of the grey-brown tomentum on pileus), whilst T. aurea has a thin cutis-like structure, resulting in a glabrous, golden yellow surface with±inflate terminal elements with granular intracellular pigmentation (Pegler 1983). Only few neotropical species of Tricholomopsis were recorded in the Neotropics, and none can be attributed to T. lechatii. Tricholomopsis tropica Dennis from Trinidad is devoid of yellow tinge in context and displays abundant hymenial gloeocystidia (Pegler 1983), what makes its classification in this genus somewhat doubtul; T. atrogrisea Pegler from Martinique, possibly more related to T. lechatii, has a gelatinized pileipellis made of adpressed hyphae; T. elegans Dennis (Dennis 1961) could be the closest relative of T. lechatii but differs at least by smaller, subglobose spores (4.5–5 µm long) and 4-spored basidia. No species described so far display either the spectacular pale grey mycelial patch observed in T. lechatii, nor its conspicuous 2-spored basidia (Fig. 1).
Figure 1 – Tricholomopsis lechatii (LIP0202264, holotype). a, b Basidiocarp c Basidiospores d Basidia e One hymenophoral hyphid. f Cheilocystidia. g Pileus covering. h Pileus margin, radial section. Drawings and macrophotos by R. Courtecuisse, microphotos by P.-A. Moreau
Figure 2 – Phylogenetic analyses were conducted online at www.phylogeny.fr (Dereeper et al. 2008). Multiple sequence alignments were performed with MUSCLE v. 3.7 (Edgar 2004). Maximum likelihood (ML) phylogenetic analysis was achieved with PhyML v. 3.0 (Guindon et al. 2010), using the GTR+I+Γ model of evolution and the Shimodaira Hasegawa version of the approximate likelihood-ratio test (SH-aLRT) of branch support (Anisimova et al. 2011). Phylogram was built using TreeDyn 198.3 (Chevenet et al. 2006) and edited with Inkscape 0.91 (https://inkscape.org/fr). Newly generated sequences for this study are in bold. The tree is rooted by a sequence of Pluteus atromarginatus (Pluteaceae)