Agonimia octospora
Agonimia octospora is a species of corticolous, squamulose lichen in the family Verrucariaceae. This minute species has a thallus made of tiny pale grey-green that are closely pressed to the bark of aged broadleaf trees, particularly oaks. It is distinguished from other members of the genus by features of its spores. The lichen occurs in ancient woodland habitats across parts of Europe and South America, showing a preference for minimally disturbed areas with abundant shrub coverage.
Taxonomy
It was formally described as a new species in 1978 by the lichenologists Brian John Coppins and Peter Wilfred James. The type specimen was collected in Glengarriff Forest in, where it was found growing on the bark of oak. Characteristics of the lichen include its colourless that number eight per ascus, and its tiny that are closely attached to its substrate. Its spores typically measure 60–75 by 20–26 μm.Description
Agonimia octospora is a minute lichen species that forms small, scattered on the bark of aged broadleaf trees, particularly oak trees. This species has several distinctive characteristics. The squamules are typically 0.05–0.1 mm thick and 0.05–0.25 mm wide, appearing pale grey-green when dry and brightening to a glaucous colour when wet. These squamules are usually closely attached to the, sometimes simple in form but occasionally irregularly divided or finger-like, with rounded or elongated shapes. Their margins may be entire or notched, and their upper surfaces are convex with a matte or slightly shiny appearance.The reproductive structures are relatively rare, scattered among the squamules, and measure 0.5–0.8 mm in diameter. They are partially embedded in the substrate, appearing spherical or somewhat pear-shaped. These structures are black with a or slightly shiny surface that may be smooth or slightly roughened. The opening appears pink-grey in immature specimens but becomes black as the perithecia mature, and is often positioned off-centre.
Under microscopic examination, the squamules are composed mostly of tissue with only a few fungal filaments penetrating the substrate. The upper surface has a single cell-thick layer with distinctive conical, peg-like projections measuring about 1–2 by 1–1.5 μm.
The wall of the perithecium comprise three distinct layers: an outer pigmented zone, an inner non-pigmented layer, and an innermost layer of inwardly directed, unbranched fungal strands. Each ascus contains 8 colourless, ellipsoid spores that are densely, typically measuring 60–75 by 20–26 μm.