Xeromphalina pseudotenuipes I. Bera & S. Khyaju, 2024

Xeromphalina pseudotenuipes I. Bera & S. Khyaju sp. nov.

( Figs. 3 View FIGURE 3 & 4 View FIGURE 4 )

MycoBank:—MB 853455

Facesoffungi Number:—FoF 15716

GenBank:—nrITS (PP622385, PP622386), nrLSU (PP622387, PP622388) and rpb2 (PP713237, PP713238)

Diagnosis:—This species of Xeromphalina can be separated from X. tenuipes by its smooth greyish yellow pileus with very crowded lamellae, smaller basidiospores, pileocystidia appearing brownish in 5% KOH, and hyphae of pileipellis and stipitipellis turning orangish brown in 5% KOH.

Type:— THAILAND. Chiang Rai Province, Mueang Chiang Rai District: Doi Hang Sub-district, N 19° 56.45466’ E 99° 40.38336’, Alt. 565 m, 12 th May 2023, I. Bera & S. Khyaju, IB 23-002 (MFLU24-0037, holotype!).

Etymology:—the epithet “ pseudotenuipes ” refers to its resemblance to Xeromphalina tenuipes .

Description:— Pileus 3–17 mm diam., convex when young, gradually becoming planoconvex to applanate on maturity, sometimes umbonate; surface moist, smooth, sub-hygrophanous; greyish yellow (4B4–5), slightly darker at the center but fading towards margin; margin entire, translucent-striate, incurved. Lamellae adnate, concolorous to pileus, very crowded (23 L+l /cm at pileus margin) when young to rather crowded (16 L+l /cm at pileus margin) when matured; lamellulae present in 5 series, concolorous; edge entire. Stipe 10–45 × 2–3 mm, central, cylindrical; surface moist, greyish yellow (4B4) at apex turning brownish yellow to golden brown (5C–D6) gradually becoming yellowish brown (5E–F6) towards base. Context in pileus thin, hollow in stipe, whitish to pale yellow (4A3), unchanging on exposure but turning yellowish brown (5F8) in 3% KOH immediately. Taste bitter. Odor indistinct. Spore print could not be obtained.

Basidiospores 3.7– 5.9 –7.9 × 2.9– 3.6 –4.2 μm (n = 30, Q = 1.19– 1.64 –1.96), ellipsoid; hyaline in 5% KOH, amyloid, thin-walled. Basidia 31.2–40.3 × 5.2–6.1 μm, subclavate, 4-spored, hyaline in 5% KOH; sterigmata 3–6.7 μm long. Basidiole 22.7–38.6 × 2.9–5.2 μm, interspersed among basidia, non-emergent, subfusoid to fusoid or lageniform, thin-walled, hyaline in 5% KOH; content like basidia. Pleurocystidia absent. Lamellae edge fertile, heteromorphous with basidia, basidioles, and cystidia. Cheilocystidia abundant, 24.2–34.3 × 2.1–3 μm, emergent up to 15 μm, coralloid with irregular branches, thin-walled, hyaline in 5% KOH. Subhymenium up to 20 μm thick, cellular. Lamellar trama composed of subparallel, hyaline, thin-walled hyphae. Pileipellis up to 250 μm thick, a cutis; suprapellis composed of loosely interwoven, sub-gelatinized hyphae with numerous scattered pileocystidia; hyphae 1.4–6.2 μm wide, thin-walled, orangish brown in 5% KOH; subpellis composed of more compactly and parallelly arranged thick-walled hyphae; hyphae 2.8–16.6 μm wide, thick-walled (0.4–1.5 μm thick). Pileocystidia abundant, 13.3–56 × 2.7–6 μm, usually cylindrical, thick-walled (upto 2 μm thick), sometimes branched, hyaline, brownish in 5% KOH. Stipitipellis a trichoderm composed of interwoven, mostly ascending hyphae intermixed with erect caulocystidia; hyphae 3.2–16.7 μm wide, thick-walled (upto 0.6 μm thick), orangish brown in 5% KOH. Caulocystidia abundant, present along the entire stipe, (22.6–) 67.5–174 × 0.8–1.3 μm, cylindrical, thick-walled (up to 1.7 μm thick), pale brownish in 5% KOH.

Habitat and distribution:—gregarious on dead, fallen and decaying bamboo logs in a mixed tropical deciduous forest.

Additional specimen examined:— THAILAND. Chiang Rai Province, Mueang Chiang Rai District: Ban Cha Lae Village, N 14° 55.1028’ E 105° 30.28254’, Alt. 495m, 23 rd June 2023, I. Bera, IB 23-020 (MFLU24-0088, paratype).

Notes:—The collybioid nature of the basidiomata, adnate attachment of the lamellae to the stipe and the bilayered nature of the pileipellis where the suprapellis is composed of thin-walled, loosely interwoven hyphae, and the subpellis is of thick-walled, more compactly arranged hyphae undoubtedly place the studied specimen of Xeromphalina under the subgenus Heimiomyces ( Singer 1962, Redhead 1988). Furthermore, the ellipsoid basidiospores, cylindrical pileocystidia, both caulocystidia and pileocystidia appearing brownish in KOH, and the occurrence with mixed deciduous forest trees classify it under subg. Heimiomyces sect. Heimiomyces (Singer) A. H. Smith. ( Miller 1968, Redhead 1988). The hyphae of suprapellis of both the pileipellis and stipitipellis turning orangish brown in 5% KOH is one of the characteristic features of the present described species. The similar-looking basidiomata, comprising ellipsoid basidiospores, coralloid cheilocystidia appearing hyaline in KOH, and a deciduous host might remind of the representative species of this section, Xeromphalina tenuipes which has its type locality in America ( Miller 1968). However, larger basidiospores [6.5–7.6(–9) × 3.5–4.5(–5) μm], the distinctive color changes of the pileipellis hyphae and pileocystidia to red, and caulocystidia to yellow-brown in KOH in X. tenuipes set it apart from the present species ( Miller 1968). To uphold these distinctions, other characteristic features of X. tenuipes such as the olive-ochraceousbrown color tones of the pileus with somewhat granulose to the rugose surface, indistinct taste, close to subdistant lamellae spacing, longer stipe (50–80 mm long) with the velvety-tomentum surface, pubescent base and tapering pseudorhiza clearly distinguishes from our described species. Another well-established and closely related taxon from subg. Heimiomyces sect. Fulvipes O. K. Miller is X. fulvipes (Murr.) A. H. Smith. Morphologically, its antler-like pileocystidia and/or caulocystidia separate X. fulvipes from the current studied species ( Miller 1968).

Besides the subgenus Heimiomyces , the basidiomata of some of the members of the subgenus Xeromphalina generally exhibit pale yellowish to brownish yellow to yellowish ochre color tones that might confuse them in the field with our studied specimen briefly. However, detailed morphological characteristics can easily discriminate the other taxa from the current species. The eccentric stipe, differently shaped cheilocystidia, pileocystidia, and caulocystidia of most widespread species, X. campanella are quite contrasting to the described specimen ( Miller 1968). Some other species previously described from Asian regions are X. aspera Maas Geest. ( Nepal), X. brevipes T. Bau & L.N. Liu ( China), X. curtipes Hongo ( Japan), X. disseminata E. Horak ( India), X. javanica E. Horak ( Indonesia), X. subsetilipes T. Bau & L.N. Liu ( China), and X. utricularis T. Bau & L.N. Liu ( China). Among these, quite a few might seem apparent similar to our described species. The yellowish brown to pale yellow basidiomata along with the pileipellis hyphae changing to orangish brown in KOH in the Chinese X. brevipes T. Bau & L.N. Liu might seem alike of the studied species ( Liu & Bau 2018). But X. brevipes differs by its eccentric and pubescent stipe, cylindrical basidiospores, dissimilar cheilocystidia, pileocystidia, and caulocystidia ( Liu & Bau 2018). The characteristic utriform cystidia of another Chinese species, X. utricularis T. Bau & L N. Liu readily demarcates from our discussed species ( Liu & Bau 2018). Xeromphalina subsetilipes , the third species described from China, shows similarity in the absence of pleurocystidia, cutis type of pileipellis where hyphae turn orangish brown in KOH ( Bau et al. 2021). Yet, the major different characters are ochraceous brown to brown pileus center, entirely pubescent stipe, setaceous caulocystidia, and encrusted hyphae in pileipellis and subpileipellis turning reddish-brown in KOH ( Bau et al. 2021). The umbilicate, yellow-brown pileus with a striate margin of X. javanica differs in its rather distant lamellae and lageniform to fusoid cheilocystidia ( Horak 1979).

Few taxa of its sister genus Heimiomyces described by Horak (1979) may resemble our studied Xeromphalina species. Heimiomyces fulvus E. Horak (1979: 142) , originally described from Papua New Guinea, may seems alike for its yellow to ochre-orangish, umbonate pileus, absence of pleurocystidia, and similar cheilocystidia but separates itself by palisadoderm (or celluloderm) pileipellis with encrusted rust brown pigment ( Horak 1979). Heimiomyces flavobrunneus E. Horak (1979: 145) ( Papua New Guinea) differs by its cylindric to fusoid cheilocystidia, caulocystidia turning pale red-brown in KOH, and pileipellis encrusted with red-brown pigment ( Horak 1979). Two more species from Papua New Guinea, H. vitiosus E. Horak (1979: 147) and H. neovelutipes (Hongo) E. Horak (1979: 148) with similar pileus colours (golden yellow and yellow-brown) distinguish by branched caulocystidia and rod-like cheilocystidia ( Horak 1979).

Therefore, our studied species is identified as a new species ( Cao et al. 2021, Chethana et al. 2021) and is named Xeromphalina pseudotenuipes sp. nov.