Nine new species in four genera of Neotropical Malpighiaceae are described and illustrated: Banisteriopsis rostrata W.R.Anderson (Brazil: Minas Gerais), Bunchosia andina W.R.Anderson (Colombia: Antioquia, Caldas, Nariño, Putomayo, Quindío, Tolima, Valle; Ecuador: Azuay, Napo, Pichincha, Tungurahua); Bunchosia parrae W.R.Anderson (Peru: Loreto, San Martín, Ucayali), Bunchosia phaeocarpa W.R.Anderson (Ecuador: Napo, Orellana, Pastaza, Sucumbíos; Peru: Loreto), Byrsonima anisophylla W.R.Anderson (Brazil: Bahia), Byrsonima cardenasii W.R.Anderson (Colombia: Antioquia, Nariño, Riseralda, Santander, Valle del Cauca), Byrsonima goiana W.R.Anderson (Brazil: Goiás), Byrsonima nana W.R.Anderson (Colombia: Meta) and Tetrapterys catarinensis W.R.Anderson (Brazil: Santa Catarina).

Two new species of Malpighiaceae are proposed: Hiraea costaricensis C.E.Anderson and H. polyantha C.E.Anderson. Hiraea costaricensis is characterised by the presence of basifixed hairs on the stems and leaves; H. polyantha, of Colombia, is distinctive in its large inflorescences, composed of c.100 flowers. Collections of the novelties had been associated with Hiraea smilacina Standl., a species that traditionally had been thought conspecific with H. quapara (Aubl.) Sprague; they are immediately separated by their fruits. In Hiraea smilacina the schizocarps break into three butterfly-shaped samaras, as is typical for the genus. The fruit of Hiraea quapara is spherical, composed of three mericarps covered by a network of reduced winglets. Hiraea smilacina is found from southern Mexico through Central America, except El Salvador and Nicaragua, and has been collected also in Colombia and Ecuador. Hiraea quapara is known mainly from French Guiana, with one collection from adjacent Suriname and two from Amapá, Brazil. All taxa are fully described and illustrated.

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.

Six new species of the Neotropical genus Tetrapterys (Malpighiaceae) are described and illustrated: T. amazonica C.E.Anderson (Brazil, Colombia and Peru), T. andersonii C.E.Anderson (Mexico), T. callejasii W.R.Anderson (Colombia), T. molinae W.R.Anderson (Honduras), T. rzedowskii W.R.Anderson (Mexico) and T. steyermarkii W.R.Anderson (Colombia and Venezuela). All have 4(–6)-flowered umbels as the ultimate inflorescence units, glabrous yellow petals, and samaras with a small dorsal wing in addition to the four large lateral wings.

Specimens of Hiraea (Malpighiaceae) from the Brazilian states of eastern Minas Gerais, Rio de Janeiro, Paraná, and Santa Catarina that had been determined as H. cuneata Griseb. and H. wiedeana A.Juss. were found to include four undescribed species. The assemblage traditionally named Hiraea cuneata includes, in addition to H. cuneata (Minas Gerais, Rio de Janeiro), two novelties: H. hatschbachii C.E.Anderson (Paraná) and H. occhionii C.E.Anderson (Rio de Janeiro). The gatherings labelled Hiraea wiedeana comprise specimens of H. reitzii C.E.Anderson (Paraná, Santa Catarina) and H. restingae C.E.Anderson (Rio de Janeiro), here newly described, and of H. macrophylla (Colla) P.L.R.Moraes & Guglielmone (Rio de Janeiro), the earlier and correct name for the species also known as H. wiedeana. In all, the flowers are borne in a single 4-flowered umbel instead of a compound arrangement, as is often characteristic of other species of Hiraea. Specimens assigned to Hiraea cuneata have the laminas abaxially sericeous initially but glabrous at maturity. In those assigned to Hiraea wiedeana the laminas are abaxially velutinous (eventually glabrescent in H. restingae). Full descriptions and synonymies are supplied, and all species are illustrated.

The assemblage of specimens from Brazil, Colombia, Ecuador, Peru and western Venezuela that had been determined as a variable species, Hiraea cephalotes Triana & Planch. (Malpighiaceae), was found to comprise seven species in addition to H. cephalotes (Colombia, Ecuador). Six are newly described: Hiraea amazonica C.E.Anderson (Brazil), H. angustipetala C.E.Anderson (Ecuador), H. breteleri C.E.Anderson (Venezuela), H. ecuadorensis C.E.Anderson (Ecuador), H. escobariae C.E.Anderson (Colombia), and H. peruviana C.E.Anderson (Peru). Hiraea spruceana var. mortoniana J.F.Macbr. is elevated to the rank of species as H. mortoniana (J.F.Macbr.) C.E.Anderson (Peru). The name Hiraea spruceana Nied. is confirmed as a synonym of H. cephalotes. All eight species are characterised by having the flowers borne in axillary, multiflowered umbels. All but one have styles with a blunt apex; in Hiraea amazonica the apex of the styles is drawn out into a short spur. All species are illustrated.