Fissurina astroisidiata is a species of lichen in the family Graphidaceae. Found in Veracruz, Mexico, it was described as new to science in 2011.[1] This lichen was the first member of its genus discovered to produce cylindrical vegetative propagules called isidia, which help it spread vegetatively without sexual reproduction. It forms pale greyish-green crusts on tree bark in shaded rainforest and produces distinctive star-shaped reproductive structures.
The lichen forms a pale gray-green to olive-green crust up to 10cm across and 100–150micrometres (μm) thick (occasionally up to 300μm where the surface is strongly blistered). The thallus is cracked and noticeably bumpy; each bump often carries a tuft of stout, tapering isidia 1–2mm long that darken at the tip as they age. In cross-section the thallus has a thin, cartilaginous cortex over an irregular algal layer peppered with clusters of calcium oxalate crystals.[2]
Reproductive structures are distinctive. The lirellae—elongate slits containing the asci—radiate from a central point on each bump, producing a star-like pattern 1–3mm long. A complete thalline rim surrounds each lirella, while the disk is partly exposed and the thin lips ( labia ) are yellow-white. Internally the exciple is colorless to orange-brown, 15–25μm thick; the hymenium stands 90–100μm high and is clear, capped by a finely granular gray-brown epithecium . Each clavate (club-shaped) ascus contains eight ellipsoid spores that are somewhat muriform (three transverse septa plus zero or one longitudinal septum per segment) and measure 12–15 × 6–8μm, roughly twice as long as wide. No secondary metabolites (lichen products) have been detected by thin-layer chromatography.[2]
Habitat and distribution
Fissurina astroisidiata is known only from the type locality in the Los Tuxtlas Biosphere Reserve, the northernmost extension of Neotropical rainforest. It grows on the bark of mature trees in the shaded understory at 1,000–1,100m (3,300–3,600ft) elevation. Because members of Fissurina typically favor long-standing, undisturbed forest, the species is considered a useful indicator of ecological continuity and forest health.[2]
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