Herpothallon polyisidiatum P. F. Chen & L. L. Zhang 2022, sp. nov.

Herpothallon polyisidiatum P.F. Chen & L.L. Zhang, sp. nov. (Figure 2)

Mycobank number: 839109

Type:— CHINA. Guangdong: Qingyuan City, Mangshan Forest Park. 1716 m elev., 24°55′22.85″ N, 112°59′35.67″ E, on bark of trees, 17 May 2019, L. S. Wang & X. Y. Wang 66649 (Holotype in KUN)

Description:—Thallus corticolous, up to 4 cm in diam., closely appressed to the substrate, firm and sometimes flaking off, minutely felty, dull, yellowish white to light yellow, in section up to 150 µm thick, with many calcium oxalate crystals in the thallus. Hypothallus byssoid, white, composed of 1–3 µm wide hyphae. Prothallus up to 1 mm broad, byssoid, composed of interwoven and radiating hyphae, whitish. Pseudisidia numerous, cylindrical, unbranched or sparsely branched, rather compact yet felty, of the same colour as thallus, up to 0.3 × 0.1 mm. Photobiont Trentepohlia, single or a few cells aggregated, cells globose, 6–10 × 5–8 µm, yellowish green. Asci and pycnidia not seen.

Chemistry and spot tests:— Thallus K+ yellow, C–, P+ orange, I–. TLC: stictic acid.

Etymology:— The epithet “ polyisidiatum ” refers to abundant pseudisidia.

Ecology and distribution: —The new species was found growing on bark of a tree in Mangshan Forest Park.

Note:—This species can be distinguished by its compact pseudisidia and the presence of stictic acid as the only metabolite. Herpothallon sticticum Jagadeesh Ram & Sinha (2011: 314), H. isidiatum Jagadeesh Ram & Sinha (2009: 611) and H. elegans G. Thor (2009: 39) also contain stictic acid, but H. sticticum has a grey to pale yellow–grey thallus and dense, minutely felty, granular globular to short cylindrical 0.05–0.1(–0.25) × 0.05–0.1(–0.2) mm wide pseudisidia with projecting hyphae (Jagadeesh & Sinha 2011); H. isidiatum has a grey to whitish grey thallus and larger pseudisidia (0.08–0.15 × 0.5–1.5 mm) with dark brown to black pycnidia at the tips (Jagadeesh & Sinha 2009); H. elegans has a hypothallus with a red layer (partly absent) and with a smooth and black layer and dark red prothallus beneath that (Aptroot et al. 2009). This species can also be confused with Diorygma antillarum (Vain.) Nelsen, Lücking & Rivas Plata (2012: 318). In Diorygma, the hypothallus is compact, not byssoid, and pseudisidia are unknown with the exception of D. antillarum, which has a distinct carbonized hypothallus, but contains different substances from H. polyisidiatum (Nelsen et al. 2012).