Athelia naviculispora S.L. Liu & L.W. Zhou, sp. nov.

Index Fungorum number: IF 901054; Mycobank number: MB 901054; Facesoffungi number: FoF 14808; Figs. 1, 2

Etymology – naviculispora (Lat.) referring to the navicular basidiospores.

Holotype – LWZ 20200921-21a (HMAS).

Diagnosis – Differing from other species of Athelia in the absence of cystidia and the presence of navicular to broadly subfusiform basidiospores.

Basidiomes resupinate, effused, thin, loosely adnate, athelioid, fragile, up to 10 cm long, 2 cm wide, 100 µm thick. Hymenophore smooth, reticulate or continuous, grayish white when fresh, pale mouse-grey to olivaceous buff when dry, not cracked. Margin thinning out as byssoid, finely fibrillose, white, 0.8 mm wide.

Hyphal system monomitic; generative hyphae without clamp connections, hyaline, thick-walled, frequently branched at right angles, 6–8 µm in diam. Cystidia absent. Basidia clavate, 4-sterigmata, simple-septate at the base, 18–22×9–13 µm. Basidiospores navicular to broadly subfusiform, hyaline, thin to slightly thick-walled, smooth, IKI–, CB–, 9–11 × 5–6 µm, L = 10 µm, W = 5.5 µm, Q =1.8 (n=60/2).

Material examined – China, Sichuan Province, Liangshan Yi Autonomous Prefecture, Leibo County, Mamize Provincial Nature Reserve, on fallen trunk of angiosperm, 21 September 2020, L.W. Zhou, LWZ 20200921-21a (HMAS, holotype); Anhui Province, Jinzhai County, Tianma National Nature Reserve, on fallen trunk of Pinus, 12 October 2020, L.W. Zhou, LWZ 20201012–13 (HMAS).

GenBank numbers – LWZ 20200921-21a : ITS= OR557252, LSU = OR527278; LWZ 20201012–13: ITS=OR557253.

Notes – Phylogenetically, Athelia naviculispora is nested within the core clade of Athelia including the generic type A. epiphylla (Fig. 3). Athelia naviculispora may be morphologically confused with A. epiphylla by grayish hymenophore and absence of cystidia; however, A. epiphylla differs in its cylindrical to ellipsoid basidiospores (Eriksson and Ryvarden 1973; Bernicchia and Gorjón 2010).

Figure 1 – Basidiomes of Athelia naviculispora (LWZ 20200921-21a, holotype). Scale bars: a=1 cm, b=1 mm

Figure 2 – Microscopic structures of Athelia naviculispora (LWZ 20200921-21a, holotype). a Hyphae from subiculum. b Basidia and basidioles. c Basidiospores. Scale bars: 10 μm

Figure 3 – Phylogeny generated by the maximum likelihood algorithm based on combined ITS and nLSU regions is presented along with the bootstrap values and the Bayesian posterior probabilities above 50% and 0.8, respectively, at the nodes. Coniophora marmorata MUCL 31667 and Pseudomerulius aureus FP-103859 were selected as the outgroup taxa. Holotypes are in bold and the newly generated sequences are in blue