Fissurina astroisidiata is a species of lichen in the family Graphidaceae. Found in Veracruz, Mexico, it was described as new to science in 2011. 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.
Fissurina astroisidiata was described in 2011 by MarÃÂa Herrera-Campos and Robert Lücking from material collected on the upper slopes of San Martin Tuxtla volcano in the Los Tuxtlas Biosphere Reserve, Veracruz, Mexico. The specific epithet combines the Latin ('star') with ('bearing isidia'), alluding to the lichen's star-shaped () and its coarse, cylindrical isidiaâÂÂthe first time true isidia have been recorded in the genus. A second isidiate species has since been discovered and described from China, Fissurina isidiata. Molecular data place F. astroisidiata at the base of Fissurina (in the strict sense, or sensu stricto), close to F. dumastii and F. crassilabra. Morphologically it most closely resembles F. incrustans and F. karnatakensis, which share gaping lirellae with thin, pale labia, but both lack isidia and differ in ascospore size or chemistry.
The lichen forms a pale gray-green to olive-green crust up to 10 cm across and 100âÂÂ150 micrometres (üm) thick (occasionally up to 300 üm where the surface is strongly blistered). The thallus is cracked and noticeably bumpy; each bump often carries a tuft of stout, tapering isidia 1âÂÂ2 mm long that darken at the tip as they age. In cross-section the thallus has a thin, cortex over an irregular peppered with clusters of calcium oxalate crystals.
Reproductive structures are distinctive. The lirellaeâÂÂelongate slits containing the asciâÂÂradiate from a central point on each bump, producing a star-like pattern 1âÂÂ3 mm long. A complete surrounds each lirella, while the is partly exposed and the thin lips () are yellow-white. Internally the is colorless to orange-brown, 15âÂÂ25 üm thick; the hymenium stands 90âÂÂ100 üm high and is clear, capped by a finely granular gray-brown . Each (club-shaped) ascus contains eight ellipsoid spores that are somewhat (three transverse septa plus zero or one longitudinal septum per segment) and measure 12âÂÂ15 à6âÂÂ8 üm, roughly twice as long as wide. No secondary metabolites (lichen products) have been detected by thin-layer chromatography.
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 elevation. Because members of Fissurina typically favor long-standing, undisturbed forest, the species is considered a useful indicator of ecological continuity and forest health.