Hymenopellis straminea Niego, & Raspé, sp. nov.  (Fig. 2-3)

MycoBank number: MB 845750; Index Fungorum number: IF 845750; Facesoffungi number: FoF 12896;

Type:—THAILAND. Chiang Rai Province: Mae Fah Luang district, elevation 1,110 m, tropical mixed deciduous forest with grass dominated by Castanopsis and Lithocarpus trees, 14 June 2019, A.G. Niego, MFLU22-0138 (holotype); GenBank OP265162-ITS, OP265157-nrLSU

Etymology:—The name refers to the straw-yellow color of the pileus of mature basidiomata.

Description: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 4–5mm width, thick, white, ventricose, adnate with no distinct decurrent tooth, spacing greater than 1 mm apart; lamellar margin even; lamellulae present, regularly arranged, in two 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 (24.5) 25.5–31–36 (43) × (12) 12.5–14–17 (18) µm an epithelioid hymeniderm with some extended pileal hairs, 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 deciduous forest of Chiang Rai Province, Thailand.

Additional specimen examined:— THAILAND. Chiang Rai Province: Mae Fah Luang district, elevation 1,100 m, tropical mixed deciduous forest, 14 June 2019, A.G. Niego, MFLU22-0139; GenBank OP265163-ITS, OP265158-nrLSU

Note: — Hymenopellis straminea is quite similar to Hymenopellis megalospora (Clem.) R.H. Petersen, the latter having usually small pileus (<50 mm) but can sometimes reach up to 120 mm diam. The color of H. megalospora could 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). The lamellae are strongly decurrent which are non-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 Hymenopellis furfuracea (Peck) R.H. Petersen having a broadly convex to nearly flat pileus with bald and moderately wrinkled surface. H. furfuracea basidiomata are more diverse in color (dark brown to grey brown or yellow brown) and size (very small to large). Lamellae also have slight decurrent tooth (Yang et al. 2009, Petersen and Hughes 2010). H. straminea on the other hand is consistently small in size (40–45 mm), straw-yellow evenly colored.

In addition, Hymenopellis raphanipes is different from the new species by having mostly dark colored basidiomata but can sometimes be “buckthorn brown” (5D6), and also vary in sizes from small to large (Petersen and Hughes 2010). Strains of H. raphanipes also have 2– and4– spored basidia, however, H. straminea is always 4–spored. When compared with H. raphanipes TENN 59800 herbarium specimen which H. straminea claded, the morphology is quite different. The most obvious difference are the basidiospores of H. raphanipes TENN 59800 which are much bigger (13.7) 14–15.8–17 (18) x (11) 12.5–13.3–14 (15) µm. The terminal elements of pileipellis of H. raphanipes TENN 59800 are also larger (20)23–37–50(70) × (10)11–14.7–17.5(21). Difference in the morphology and supported by high genetic distance in the clade concluded that indeed H. straminea is a novel species.

Figure 1. Basidioma of Hymenopellis straminea. A,B,D top view of basidiomata C view of lamellae Scale bar: 3 cm (A–D) Photographs by A.G. Niego

Figure 2. Microscopic characters of H. straminea. A basidiospores B basidia C cheilocystidia D pleurocystidia E pileipellis F stipetipellis