Parmotrema lichexanthonicum is characterized by the presence cespitose cilia, medulla with lichexanthone and salazinic acid, and the absence of vegetative propagules.
The presence of cespitose cilia in this species is notorious and was already pointed out by Ribeiro (1998). It is correlated with the presence of lichexanthone in the medulla. Similar species with salazinic acid and lichexanthone include P. pontagrossense and P. spinibarbe (sorediate), and P. ultralucens (isidiate).
While identifying specimens of Parmotrema lichexanthonicum, we realized that the medulla not always shows an evident yellow bright under the UV lamp. Donha (2005) noticed the same for P. pontagrossense and suggested the TLC analysis as essential to assure the presence of lichexanthone. However, the experience has demonstrated that the presence of cespitose cilia together the typical dark reddish brown shiny marginal zone are strong indication of the medullar lichexanthone presence in Parmotrema species.
An important and relatively recent problem is the exploration of Brazilian lichens in a commercial scale. Christensen & Sipman (1998) noted that Brazilian lichens were sold in European markets. They thought that one of the species was Parmotrema cetratum (Ach.) Hale. However, close examination of the specimens deposited in C Herbarium proved they are actually Parmotrema lichexanthonicum. So, it is possible that this apparently endemic lichen be an endangered species.