The type specimen was collected from within the state of Rondônia at the Sítio Ecológico Buriti, located on Lago Cujubim, northeast of Porto Velho.

[1] Pseudopyrenula flavoreagens is characterised by a thallus that lacks a protective outer cortex, presenting a dull and continuous surface that can cover areas up to 2 cm in diameter.

Its colour is a whitish grey, distinctly outlined by a black line known as the hypothallus, approximately 0.2 mm wide, which does not lead to the formation of galls (abnormal growths) on the host bark.

The wall of these structures is carbonised, up to 40 μm thick, with the ostioles (openings) located at the top, remaining separate, flat, and black in colour.

The spores have pointed ends, diamond-shaped internal spaces (lumina), and are partly yellow, lacking a gelatinous surrounding layer.