Cruentotrema amazonum is a little-known species of script lichen in the family Graphidaceae. It is found in Brazil, Thailand, and Vietnam, where it grows in the understory of primary rainforests.
The lichen was formally described as a new species in 2014 by lichenologists Marcela Cáceres, André Aptroot, and Robert Lücking. The type specimen was collected by the first two authors from the at an altitude of 100m (300feet), where it was found in understory of a primary forest growing on tree bark. The taxon was placed in Graphidaceae genus Cruentotrema because of the morphology of its ascoma, and its, non-amyloid ascospores.
Cruentotrema amazonum is a corticolous (bark-dwelling) lichen that grows partially endoperidermal (i.e., beneath the surface of the) and has a smooth to uneven dark olive-green surface. The thallus is up to 10abbr=onNaNabbr=on in diameter and is continuous. The partner for this lichen is Trentepohlia (a genus of green algae), and the lichen lacks crystals between the and . Ascomata are rounded to angular,,, and have a complete . The of the ascomata are partially exposed; they are light grey-brown and translucent. The is distinct and fissured-lobulate, visible as triangular initially covering the disc, grey-brown, fused with inner portions of the thalline margin but splitting from outer portions. The is entire and brown or becoming in the upper half. asci have a fusiform to shape, and the are ellipsoid, contains 3 septa, and measure 15–20 by 6–8 μm.
Cruentotrema amazonum was first described from primary rainforests in the state of Rondônia, Brazil, where it occurs in the shaded understory. In 2017, it was reported from Vietnam, and in 2022 from Thailand. The latter report was the first documented record of a Cruentotrema in Thailand.