This species is weedy and quite commonly collected, and widespread worldwide. It is characterized by herbaceous, sprawling to prostrate habit; generally rather dense hispid to pilose or hirsute pubescence; terminal, subcapitate, several-flowerewd inflorescences usually subtended by two decussate pairs of ovate bracts; generally 6-merous flowers; a pink to white corolla 2-8 mm long; and fruits with usually 3 mericarps. The mericarps are elliptic to obovate in outline, abaxially hispidulous to strigose or hispid, and adaxially have two broad concave faces separated by a medial ridge. This is one of the two most commonly collected species of Richardia.
Richardia brasiliensis is similar morphologically similarly adventive, and similarly common to Richardia scabra and Richardia grandiflora, and these are often confused. Problematically these are confidently separated mainly by mature mericarp morphology and sometimes by mature corollas, and a number of specimens of all of these species lack either of these. Richardia grandiflora is has corollas 8-25 mm long and mericarps that have a medial sulcus and are scattered- to densely tuberculate abaxially. Richardia scabra has flowers of similar size to Richardia brasiliensis but mericarps that are abaxially hispidulous to papillose or tuberculate and adaxially has a medial sulcus.
Richardia lomensis is also similar to Richardia brasiliensis. This other species is separated by its short stature, and habitat and range in the coastal lomas (fog deserts) of southwestern Peru.
Several specimens are unusual in having elongated stems, relatively smaller leaves and heads than average for Richardia brasiliensis, 6-merous flowers, white corollas 4-5 mm long, and mericarps that are distinctive. These have two broad adaxial excavations separated by a medial ridge and abaxially are rounded and smooth. The general characters of these plants agree with Richardia brasiliensis, but the relatively small leaves and heads and the smooth, usually rounded abaxial side of the mericarps are similar to species of Subg. Asterophyton. Specimens with these characteristics are from sporadlic, widely separated localities, at least some of them areas where species of Subg. Asterophyton are apparently sympatric (Argentina: Salta; Bolivia: Chuquisaca, La PazlTarija; Brazil: Bahia).
The names Richardsonia adscendens DC. and Richardia adscendens (DC.) Steud. were treated by Lewis & Oliver as synonyms of Richardia brasiliensis, but the illustration in the MO collection was identified as Richardia scabra by W.H. Lewis. No original material has been seen in this study, and the identity of Candolle's name is not yet entirely clear; if the material on which this name was based was actually from Mexico, it is much more likely to have been Richardia scabra though it could have been Richardia brasiliensis.