Fissurina flavomedullosa is a species of crustose lichen-forming fungus in the family Graphidaceae. It is a bark-dwelling lichen with a distinctive yellow inner tissue (medulla) and narrow, slit-like fruiting bodies, known from lowland rainforest in Amazonian Peru. The species was described in 2012 and is named for its unusually colored medulla.
Fissurina flavomedullosa was described as new to science in 2012 by Eimy Rivas Plata and Robert Lücking from material collected in Amazonian Peru. The species epithet refers to its yellow medulla.
The thallus is crustose and grows on bark. It is green-gray, continuous, and up to 10 cm across and 60âÂÂ120 üm thick, with a smooth to uneven surface and a dense . The is from the green algal genus Trentepohlia; the has scattered clusters of calcium oxalate crystals. The medulla is yellow, and the base includes a strongly (blackened) layer about 20âÂÂ30 üm thick.
The fruiting bodies () are wavy () and irregularly branched, ranging from sunken in the thallus to partly protruding (immersed to ), and slit-like (), with a complete covering of thallus tissue (). They are 1âÂÂ2 mm long and 0.07âÂÂ0.1 mm wide, with the hidden from view; the lips () are thin and not frosted (non-). The spore-bearing layer (hymenium) is 80âÂÂ100 üm high. Each ascus contains eight oval (ellipsoid), 4-celled (3-septate) ascospores measuring 10âÂÂ13 à5âÂÂ6 üm. The spores have a thick outer wall and thick cross-walls, and stain violet-blue with iodine (I+ violet-blue). Chemically, the inner tissue (medulla) contains a yellow anthraquinone pigment (reacting K+ orange-red).
The species is known from the Los Amigos Research and Training Center (CICRA) in Madre de Dios, Peru, at about elevation in tropical lowland rainforest. The type collection was made on tree bark in secondary forest in August 2008.