Myriostigma melanovillosa J. X. Xue & Lu L. Zhang, 2025

Xue, Junxia, Yang, Zihao, Li, Ruotong & Zhang, Lulu, 2025, Four new species of Cryptothecia (Arthoniaceae, Ascomycota) and Myriostigma (Arthoniaceae, Ascomycota) from China, based on morphology and molecular phylogeny, MycoKeys 114, pp. 367-383 : 367-383

Myriostigma melanovillosa J. X. Xue & Lu L. Zhang sp. nov.

Fig. 4

Diagnosis.

The new species differs from other species of Myriostigma in the presence of black or purple dots on the thalli and hyaline to pale yellow ascospores (63–71 × 26–33 µm).

Type.

China • Yunnan Province, Xishuangbanna Dai Nationality Autonomous Prefecture, Jinghong City, Primitive Forest Park , 22°1'55.75"N, 100°52'37.47"E, alt. 689 m, on the bark of trees, 7 March 2023, L. L. Liu et al. 20230635 ( SDNU, holotype) .

Description.

Thallus corticolous, up to 6 cm in diameter, ecorticate, cottony, dull, greenish grey to whitish grey, with black or purple dots, firmly attached to the substrate. Isidia not observed. Prothallus is usually distinct, thin, whitish byssoid, mainly composed of interwoven and radiating hyphae, 0.7–1.3 mm wide, forming a dark brown to black line while bordering different species. Medulla white, with calcium oxalate crystals. Photobionts trentepohlioid, cells rounded to elliptical, single or a few cells aggregated, 5–11 × 5–8 µm. Hyphae 1–2 µm wide.

Ascigerous areas are distinct, generally delimited, erumpent, slightly raised above the thallus level, plaque, irregular in outline, white with dense brown dots indicating individual asci. Asci frequent, hyaline, pale yellow when mature, globose to subglobose, often covered by hyaline hyphae, 8 - spored, 103–115 × 97–115 µm. Ascospores hyaline, pale yellow when mature, oblong, muriform, curved, often broader in the centre, 63–71 × 26–33 µm.

Pycnidia were not observed.

Chemistry.

thallus C + red, K –, P –, UV + pale grey-white; medulla and paraphysoids I + sky-blue. TLC: gyrophoric acid, lecanoric acid and confluentic acid.

Etymology.

The epithet refers to the presence of black or purple dots on the thallus.

Ecology and distribution.

This species is found only in China on the bark of trees in a humid tropical forest in Yunnan Province.

Notes.

Morphologically, Myriostigma melanovillosa is similar to M. irregularis Lücking, Aptroot, Kalb & Elix , as they both have irregular erumpent and with brown dots whitish ascigerous areas, but M. irregularis has narrower asci (40–70 µm wide) and psoromic acid, subpsoromic acid, 2 ′ - O - demethylpsoromic acid and trace confluentic acid as secondary metabolites ( Lücking et al. 2006).

Phylogenetically, Myriostigma melanovillosa is clustered with Stirtonia neotropica Aptroot. They both have C + red thalli and 8 - spored asci, but S. neotropica has linear shape ascigerous areas, ovoid asci and transversely septate ascospores (35–38 × 10–12 µm) ( Aptroot 2009).

Additional specimens examined.

China • Yunnan Province, Xishuangbanna Dai Nationality Autonomous Prefecture, Jinghong City, Primitive Forest Park , 22°1'55.75"N, 100°52'37.47"E, alt. 689 m, on the bark of trees, 7 March 2023, L. L. Liu et al. 20230629 ( SDNU) ; • ibid., 20234628 ( SDNU) .

Figures

Figure 4. Myriostigma melanovillosa (SDNU 20230629, type for (A, B); SDNU 20230635, holotype for (C, D, E, F )) A prothallus B black or purple dots C thallus D ascigerous areas E asci F ascospores. Scale bars: 200 µm (A, B, D); 500 µm (C); 10 µm (E, F).