Aspidothelium glabrum
Aspidothelium glabrum is a species of corticolous, crustose lichen in the family Thelenellaceae. It was described in 2008 from material collected on bark in western Costa Rica, and has since been recorded in Brazil. The lichen forms pale mineral-gray patches that may be edged by a thin black border, and it produces tiny, glossy, cream-to-gray bumps on the surface that contain its spores. Under the microscope, its spore-producing sacs contain four colorless spores that are divided into many small compartments, a feature used to separate it from similar species.
Taxonomy
It was described as a new species in 2008 by the lichenologists Robert Lücking, André Aptroot, and Harrie Sipman, based on material collected on bark in Carara National Park in Puntarenas Province, Costa Rica at elevation.Description
The lichen has a pale mineral-gray thallus that is often partly immersed in the substrate, and it can be edged by a narrow black line of up to 0.2 mm wide. Its perithecia sit directly on the surface as smooth, hemispherical to barrel-shaped structures about 0.2–0.4 mm across. They are pale cream to gray and glossy, becoming brownish gray toward the top, and each has a depressed black ostiole ; in cross section, the ostiole appears as a black cap set slightly below the perithecial apex.Microscopically, the tissue between the asci is not oil-filled, and its filaments can be partly branched. Each ascus contains four hyaline spores that are fusiform and densely, with 7–9 transverse septa and 1–3 longitudinal septa, some of them oblique; the spores measure about 40–50 × 12–15 μm. In the original description, this combination of muriform spores and unadorned perithecia was treated as distinctive within Aspidothelium. The authors said it most closely resembles Aspidothelium geminiparum, but that species has spores divided only by cross-walls. They also noted it could be mistaken for Thelenella paraguayensis; however, that species hides its perithecia in wart-like bumps of the thallus and has a branching network of hyphae between the asci that often join, along with spores that have rounder ends.