Polymeridium albidoreagens is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae. Found in Brazil, it was formally described as a new species in 2013 by lichenologists André Aptroot, Aline Anjos Menezes, and Marcela Cáceres. The type specimen was collected in Rondônia's Porto Velho, Parque Natural Municipal, at an altitude of ; other specimens have been reported from Ceará in the Chapada do Araripe. This lichen species is similar to Polymeridium albidum but is characterized by its UV+ (yellow) thallus. The , whitish-grey thallus features spherical, , solitary ascomata with diameters ranging from 0.2 to 0.4 mm and an apical ostiole. The is not , and the number 8 per ascus, contain 3 septa, and measure 20âÂÂ23 by 6âÂÂ8 üm without ornamentation. The lichen's chemistry includes the presence of lichexanthone.