The Neotropical genus Mezia (Malpighiaceae) comprises 15 species of lianas (except M. huberi W.R.Anderson, a shrub or small tree). All have multibranched, densely brown-sericeous inflorescences with the ultimate unit a 4-flowered umbel of bilaterally symmetrical flowers. The distinctive pair of large cymbiform bracteoles subtends a rudimentary pedicel and encloses the floral bud. The flowers contain elongate sepals, the lateral four biglandular, yellow petals, the posterior often splotched with red, a heteromorphic androecium, and a tricarpellate gynoecium. The three styles are all free; the posterior pair is lyrate in five species but erect in the others. The samaras have an orbicular to oblate lateral wing and a much smaller dorsal wing; in most species, additional winglets and/or crests are present between the lateral and dorsal wings. Only Mezia mariposa W.R.Anderson has butterfly-shaped samaras lacking additional ornamentation. Four new species are proposed: Mezia andersonii C.E.Anderson, M. bahiana C.E.Anderson, M. fanshawei C.E.Anderson and M. sericea C.E.Anderson. One variety is elevated to species level and provided with a new name, Mezia peruviana C.E.Anderson; a lectotype is chosen for Diplopterys involuta var. ovata Nied. Full descriptions and synonymies are provided, as well as a distribution map. All species are illustrated.