Hymenopellis straminea

Hymenopellis straminea Niego & Raspé,

MycoBank No: 845750, Facesoffungi Number: FoF12896

Basidiomata small-sized. Pileus 35–45 mm diam., circular in polar view, in side view convex to applanate, straw-yellow or buff (4B5) evenly colored but darker when young; surface dry to viscid, sticky when wet, non-hygrophanous, rugulose, moderately wrinkled; margin decurved to plane, translucent striate; context white, unchanging when cut, consistency rubber-like. Lamellae 4–5 mm broad, thick, white, ventricose, adnate with no distinct decurrent tooth, spacing > 1 mm; lamellar margin even; lamellulae present, regularly arranged, in 2 (3) tiers. Stipe 65–85 × 3–4 mm, central, cylindrical, mostly equal, thickened at the base, light brown, lighter (5A2) from the pileus becomes yellowish brown (5D5) towards the base, surface dry, appressed squamulose especially towards the base, fistulose; context white, unchanging when cut; pseudorrhiza present. Spore print white. Smell indistinct. Taste mild. Basidiospores [60,2,2] (9)10.2–12.8–14.5(15) × (8)8.5–11–11.5(12) μm (Q = 1.0–1.3, Q* = 1.2), subglobose to ellipsoid, thin-walled, hyaline in 5% KOH. Basidia [30,2,2] (35)36–42.8–57(60) × 12–14.3–20 μm (Q = 2.7–3.3, Q* = 3.0), tetrasporic, clavate, without clamp connection; contents grossly granular. Cheilocystidia [30,2,2] (21)26–47–73.5(74) × (6)9.5–12.5–18(21) μm (Q = 2.1–6.2, Q* = 3.8), numerous, grouped together, pedunculate, narrowly lageniform, clavate to broadly clavate, fusiform, smooth, thin-walled, hyaline in 5% KOH. Pleurocystidia [30,2,2] (48.5) 55–87–136 (168) × (15.5) 16–21.5–29 (32.5) μm (Q = 2.5–5.8, Q* = 3.6), mostly narrowly lageniform but can also be fusiform, smooth, thin-walled, hyaline in 5% KOH. Hymenophoral trama irregular, made of thin-walled, hyaline hyphae. Pileipellis an epithelioid hymeniderm with some extended pileal hairs; terminal elements (24.5)25.5–31–36(43) × (12)12.5–14–17(18) μm, with scattered intracellular light brown (6D8) pigment in 5% KOH. Stipitipellis a cutis; hyphae (7.5)8–9.5–11.5(12) μm wide, with intracellular light brown (6D8) pigment in 5% KOH. Clamp connections were seen in the lower part of the stipe.

Habitat and distribution: Solitary, in tropical hill forest of Chiang Rai Province, Thailand.

Additional specimen examined: Thailand. Chiang Rai Province: Mae Fah Luang District, elev. 1,100 m, tropical hill forest, 14 June 2019, A.G. Niego, MFLU22-0139; GenBank OP265163-ITS, OP265158-nrLSU.

Notes: Hymenopellis straminea is quite similar to H.megalospora (Clem.) R.H. Petersen, the latter having usually small pileus (<50 mm) but H. megalospora can sometimes reach up to 120 mm diam. The color of H. megalospora may range from disc deep olive brown to “buckthorn brown” (5D6) to pale ochraceous buff (4A2), to nearly white, with or without a darker center. The stipe of H. megalospora, however, is quite longer (70–250 × 2–3 mm), and the lamellae are strongly decurrent, which is not evident in H. straminea. Moreover, H. megalospora has larger basidiospores (15–21 × 8–12 µm) which are finely dimpled or pitted (Petersen and Hughes 2010). Hymenopellis straminea is also quite similar to some specimens of H. furfuracea (Peck) R.H. Petersen in having a broadly convex to nearly flat pileus with bald and moderately wrinkled surface. Hymenopellis furfuracea basidiomata are more diverse in color (dark brown to gray brown or yellow brown) and size (very small to large). Lamellae also have slight decurrent tooth. Hymenopellis straminea on the other hand is consistently small in pileus size (35–45 mm), evenly straw-yellow. Finally, Hymenopelli sraphanipes is different from the new species by having mostly dark colored basidiomata but they can sometimes be “buckthorn brown” (5D6), and also vary in size from small to large (Petersen and Hughes 2010). Strains of H. raphanipes also have 2- and 4- spored basidia. H. straminea basidia, however, are always 4-spored. When compared with H. raphanipes TENN 59800, the herbarium specimen with which H. straminea formed a clade, the morphology is quite different. The most obvious difference is the much bigger basidiospores of H. raphanipes TENN 59800 [(13.7) 14–15.8–17 (18) × (11) 12.5–13.3–14 (15) µm]. The terminal elements of the pileipellis of H. raphanipes TENN 59800 are also larger [(20)23–37–50(70) × (10)11–14.7–17.5(21) µm]. Those morphological differences, together with the high genetic distance in the clade, support that H. straminea is a novel species.

Fig. 1 Phylogenetic tree generated from ML analysis of combined ITS and nrLSU data set for Hymenopellis with three outgroup species. Bootstrap support values (≥70%) and posterior probabilities (≥0.9) (BS/PP) are given above the branches. All termini are with species name and voucher ID, with the newly generated sequences from this study in bold.