Fissurina microcarpa

The thallus of F. microcarpa forms a brown, glossy crust that becomes cracked and warted as it ages. Across this surface develop plentiful lirellae: minute, cinnamon-brown fissures measuring 0.1–0.4 mm long that may stay simple or fork into short branches. Each lirella is immersed at first, then rises slightly as the surrounding cortex swells and splits; its walls (the exciple) are pale orange-brown and lack the blackened carbon layer (carbonisation) seen in some relatives.^[2]

Internally the colourless hymenium (spore-producing tissue) stands 112–150 μm tall, and the asci are distinctive in containing a single ascospore rather than the usual eight. That spore is large (87–125 μm long), muriform—divided into many brick-like chambers by both cross-wise and length-wise septa—and wrapped in a gelatinous halo 5–8 μm thick that becomes visible in water mounts. Chemical spot tests show the presence of stictic acid; this secondary metabolite helps separate the species from superficially similar taxa that lack lichen products.^[2]

Fissurina microcarpa is known only from two localities in the central and southern Western Ghats of India: the type locality at Upper Kodayar, Tamil Nadu, and an additional site near Sringeri–Balehonnur in Karnataka. Both lie within humid evergreen or semi-evergreen hill forests that receive heavy monsoon rainfall. The lichen grows on the bark of living trees in shaded, mossy situations.^[2]