Astrothelium caucavallense Soto-Medina & Aptroot 2023

Astrothelium caucavallense Soto-Medina & Aptroot, sp. nov.

(Fig. 1)

A new Astrothelium similar to A. megaeneum Flakus & Aptroot, but differs by its larger ascospores.

HOLOTYPE. — Colombia. Valle del Cauca, Municipio Roldanillo, corregimiento Higueroncito, 4°29’52.2”N, 76°06’39.1”W, 998 m, tropical dry forest, 16.XI.2020, Soto Medina 28H (holo-, TULV).

ISOTYPE. — Colombia. Valle del Cauca, Municipio Roldanillo, corregimiento Higueroncito, 4°29’52.2”N, 76°06’39.1”W, 998 m, tropical dry forest, 16.XI.2020, Soto Medina 82H (iso-, CUVC).

ETYMOLOGY. — The epithet refers to refers to the Valle del Cauca, a department in Colombia.

ECOLOGY. — This species grows on bark of Zanthoxylum caribaeum Lam. and Euphorbia cotinifolia L. in tropical dry forest.

CHEMISTRY. — Thallus UV– but orange pruina UV+ red, K+ red, C–; medulla C–, K–, KC–; orange pruina on pseudostromata surface UV+ red, K+ red.

MYCOBANK. — MB 849069.

DESCRIPTION

Thallus corticolous, crustose, corticate, smooth, (olive-)green but partially covered by orange pruina. Photobiont of a species of Trentepohlia Martius. Ascomata globose in section, 0.5-1.0 mm diam., single to laterally aggregated, immersed in weakly delimited pseudostromata, their base often immersed in the bark; pseudostromata covered by orange pruina. Perithecial wall fully carbonized, up to up 100 µm wide. Ostioles apical, not fused, appearing as flat, dark brown spots from above. Hamathecium not inspersed. Asci 8-spored. Ascospores hyaline, 3-septate, oblong, 35-50 × 11-15 µm, their ends rounded and their lumina diamond-shaped, surrounded by a gelatinous layer up to 10 µm thick. Pycnidia not observed.

NOTES

With the external orange pigment produced on the thallus and particularly the pseudostromata, Astrothelium caucavallense Soto-Medina & Aptroot, sp. nov. belongs in the A. aeneum complex, but within which it is distinguished by its comparatively large ascospores. Most species in this complex have small ascospores around 20-25×6-10 µm large; the only species so far known with somewhat larger ascospores (25- 35× 10-12 µm) is A. megaeneum Flakus & Aptroot, but even in that species, the ascospores are considerably smaller than in the new species (Aptroot & Lücking 2016). Within the A. aeneum complex, species either have a clear or an inspersed hymenium. An inspersed hymenium is found in A. inspersaeneum E.L.Lima, Aptroot & M.Cáceres and A. aenascens Aptroot, both with small ascospores, whereas a clear hymenium is found in A. aeneum (Eschw.) Aptroot & Lücking (small ascospores), A. megaeneum (ascospores of intermediate size), and in the new species, with large ascospores, all with a similar overall morphology (Aptroot & Lücking 2016). The new species would key out in the recent world key to the family (Aptroot 2021) in couplet H31, with: ascospores 35-50 µm long.