Mycobank MB 517767
Thallus superficially delimited by yellowish-grey color and partially a thin, brown-black prothallus, but proper thallus structures (cortex, algal layer, medulla) absent; photobiont a species of Trentepohlia, cells 7–12 × 7–9 µm, located within the periderm cells of the tree bark and connected to the base of the apothecia by hyaline fungal hyphae. Apothecia erumpent from periderm and finally almost appearing sessile, rounded, up to 1 mm diam., with brown-black disc and irregular marginal, grey-white lobules (remnants of the initially covering periderm). Proper excipulum 20–40 µm broad, red-brown, lateral towards the hymenium with anastomosing periphysoids and paraphysoids. Hymenium 55–70 µm high, non-amyloid, composed of unbranched to rarely anastomosing paraphyses; asci ellipsoid to clavate, 55–65 × 15–18 µm, non-amyloid, with thick tholus and distinct ocular chamber when young (probably fissitunicate). Ascospores 8 per ascus, ellipsoid, 1-septate, 15–20 × 6–8 µm, hyaline, non-amyloid, constricted at septum when mature. Secondary chemistry: no substances detected by TLC.
Eremithallus is a recently described genus that appears to represent a distinctive lineage within the higher Ascomycota (Lücking et al., 2008b). Morphologically and anatomically it resembles Ostropales (Lecanoromycetes), but genetically clusters outside that class. Unique features of the genus are the absence of a lichen thallus, the photobiont cells instead clustered in distinct, discrete groups within dead periderm cells of the tree bark, the laterally strongly anastomosing periphysoids, and the ascospores containing folds or crystals, at least in the type species. The genus superficially resembles non-lichenized fungi such as Dothidea and Melaspilea, but these differ anatomically in the structure of the hymenia and/or stromata. The new species differs from the type species mainly in the smaller ascospores (20–30 µm long in E. costaricensis) which lack folds. Also, the hymenium is lower and the asci are smaller on average. Otherwise, the apothecial anatomy, especially the thin brown excipulum bordering a layer of strongly anastomosing periphysoids (or lateral paraphyses), as well as the peculiar position of the photobiont, agree in both taxa. While in the type species, only mature asci where observed, the new species also showed young asci with a typical fissitunicate anatomy. It is not unlikely that an older name is available for this genus, but thus far we have not been able to detect anything similar described in the literature or among revised herbarium collections.
We honour our mentor and colleague, María de los Angeles Herrera Campos, for her contributions to lichenology in Mexico.
Eremithallus marusae is known from Chamela-Cuixmala Biosphere Reserve in Jalisco, Mexico, which is one of the last protected areas of tropical deciduous dry forest remaining in the Neotropics. The reserve bears a unique and highly diverse lichen biota with dominance of crustose taxa (Miranda et al., 2009). Both known species of Eremithallus seem to prefer (semi-)deciduous dry forest vegetation.
Type:—MEXICO: Jalisco: Estación de Biología Chamela, tropical deciduous dry forest, 19° 29’N, 105°02W, 60 m, June 2009, Miranda 766 on bark of Heliocarpus pallidus (holotype MEXU).
Additional specimens examined (paratypes):—MEXICO: Jalisco: Estación de Biología Chamela, Miranda 767, 1328, 1331 (MEXU).