Calocybella sribuabanensis N. Suwannarach, J. Kumla and S. Lumyong, sp. nov.

Index Fungorum number: IF 559933; Mycobank number: MB 559933; Facesoffungi number: FoF 12909; Fig. 1

Etymology – “sribuabanensis” referring to Sri Bua Ban Subdistrict where holotype was found.

Holotype – SDBR-CMUNK0910.

Basidiomes small, collybioid. Pileus 10–25 mm broad, convex or hemispherical when young, becoming campanulate and finally plano-convex with a small indistinct umbo; surface initially reddish brown (7E7) to brown (7E8) except at the margin which is grayish orange (5B6), not striate, somewhat granulose all over; margin initially incurved, becoming decurved to somewhat straight with age, slightly wavy or somewhat lobate. Lamellae emarginate with a small decurrent tooth, moderately crowded, initially grayish yellow (4B6), becoming light yellow (4A5) at maturity, up to 3 mm wide, with lamellulae of 3–6 lengths; edge finely torn, concolorous with the sides. Stipe 20–32 × 3–4 mm, central, terete or slightly compressed, equal or slightly tapering towards the base, stuffed; light yellow (4A4) to grayish yellow (4B5), appressed-fibrillose all over; base slightly enlarged, whitish. Context up to 2 mm thick at the center of the pileus, light yellow (4A4). Odor not distinctive.

Basidiospores 5–8×3–5 μm, Q=1.33–2.00, Qm =1.65, ellipsoid to oblong-ellipsoid, with a fine verrucose ornamentation, hyaline, thin- to slightly thick-walled, acyanophilous, inamyloid. Basidia 22–25×7–8 μm, clavate or rarely pedicellate-clavate, hyaline, thin-walled, 4-spored, rarely 2-spored; sterigmata up to 6 μm long. Lamella-edge fertile. Pleurocystidia and cheilocystidia absent. Lamellar trama subregular to almost regular; hyphae 3–6 μm wide, hyaline, thin-walled, not discoloring in KOH, inamyloid. Pileus trama interwoven; hyphae 4–10 μm wide, with a pale yellowish brown wall pigment which is darker towards the pileipellis, thin-walled, not discoloring in KOH, inamyloid. Pileipellis a cutis; hyphae 3–5 μm wide, with a pale yellow wall pigment, thin-walled, slightly gelatinized. Stipitipellis a cutis composed of narrow, interwoven hyphae coated with a resinous material; hyphae 3–7 μm wide, with a pale yellow wall pigment which is paler towards the stipe base, thin-walled. Caulocystidia absent. Clamp connections observed on all hyphae.

Habitat and distribution – Solitary to gregarious on soil. Known only from Thailand.

Material examined – Thailand, Lamphun Province, Sri Bua Ban Subdistrict, Chiang Mai University Haripunchai Campus, 18°32′18″N 99°7′2″E, elevation 368 m, solitary to gregarious on soil, 16 August 2020, J. Kumla and N. Suwannarach, SDBR-CMUNK0910 (holotype); 18°32′19″N 99°7′4″E, elevation 371 m, solitary to gregarious on soil, 19 August 2022, J. Kumla and N. Suwannarach, SDBR-CMUNK1783.

GenBank numbers – SDBR-CMUNK0910: ITS=OP503445; SDBR-CMUNK1783: OP503940.

Notes – Phylogenetic analysis of the ITS sequence confirmed that C. sribuabanensis stands within the genus Calocybella and clearly separate from the other Calocybella species (Fig. 2). This is the first record of the genus Calocybella from Thailand. Morphologically, C. sribuabanensis is similar to C. goethei; however, C. goethei has a longer stipe (30–45×3–5 mm) than C. sribuabanensis (20–32×3–4 mm, Crous et al. 2021b). A phylogenetic tree showed that C. sribuabanensis and C. goethei formed distinct species. Calocybella sribuabanensis forms a sister taxon to C. dicholamellata known from India with high support value (100% BS and 1.00 PP, Latha et al. 2020). However, the latter species is distinct by its brownish yellow pileus and narrower size of basidia (20–25×5–7 μm, Latha et al. 2020). An ITS sequence of C. sribuabanensis exhibit 97.68% similarity with both sequences of the C. dicholamellata CAL1242 (holotype) and DKP522.

Figure 1 – Calocybella sribuabanensis (SDBR-CMUNK0910, holotype). a Basidiomes. b Basidiospores. c Basidia. d. Pileipellis hyphae. Scale bars: a=10 mm, b, d=5 μm, c=10 μm

Figure 2 – Phylogenetic tree derived from maximum likelihood analysis of ITS gene of 30 sequences and the aligned dataset was comprised of 804 characters including gap. The average standard deviation of the split frequencies of the BI analysis was 0.00893. A best scoring RAxML tree was established with a final ML optimization likelihood value of -6247.2241. The matrix had 511 distinct alignment patterns with 18.35% undetermined characters or gaps. Estimated base frequencies were found to be: A=0.2542, C=0.2004, G=0.2186, T=0.3266; substitution rates AC=1.5589, AG=4.1460, AT=1.7968, CG=0.7747, CT=5.1818, GT=1.0000. Entoloma hainaense GDGN 27990 and E. tiliae LE254179were used as outgroup. Numbers above branches are the bootstrap statistics percentages (left) and Bayesian posterior probabilities (right). Branches with bootstrap values≥70% and PP≥0.90 are shown at each branch. The bar represents 0.1 substitutions per nucleotide position. Type strains are in bold. The newly generated sequences are indicated in blue