Platythecium hypoleptum is a species of corticolous (bark-dwelling), crustose lichen in the family Graphidaceae.
The lichen was first formally described as a species new to science in 1863 by Finnish botanist William Nylander, as a member of the genus Graphis. The type specimen was collected in Nova Granada (Brazil), at an altitude of 2400m (7,900feet). Nylander noted some similarity with Graphis homographiza, and also compared it to Graphis dividens (now Phaeographis dividens). In 2002, Bettina Staiger proposed a transfer to genus Thalloloma, based on a reorganisation of family Graphidaceae that stressed the importance of ascocarps and their accessory organs as characteristics to delimit genera. A year later, Minoru Nakanishi and Hiroyuki Kashiwadani suggested that the taxon should instead be in genus Platythecium.