Diplostephium comprises 111 neotropical species that live in high elevation habitats from Costa Rica to Chile. Primarily Andean, the genus seems to have undergone an adaptive radiation indicated by its high number of species, broad morphological variation, and diversification primarily in an ecosystem (páramo) that formed within the last 2–5 my. Internal transcriber spacer (ITS) sequences and several chloroplast markers, rpoB, rpoC1, and psbA-trnH were sequenced in order to infer a preliminary phylogeny of the genus. The chloroplast regions showed no significant variation within the genus. New ITS data were therefore analyzed together with published sequences for generating a topology. Results suggest that Diplostephium and other South American genera comprise a polytomy within which a previously described North American clade is nested. Monophyly of Diplostephium was neither supported nor rejected, but the formation of a main crown clade using different methods of analysis suggests that at least a good portion of the genus is monophyletic. A Shimodaira-Hasegawa test comparing the topology obtained and a constrained one forcing Diplostephium to be monophyletic showed no significant difference between them. Monophyly of some of the previously proposed series of the genus was not supported by the phylogenetic tree. Morphological character mapping results suggest that the high Andean forest tree species are derived from shrubby páramo-puna ancestors, contradicting previous hypotheses about morphological evolution of the genus and documenting an atypical trend of downslope diversification in páramo plants.

Justicia salasiae, a new species from tropical deciduous forests in the Sierra Madre del Sur of southern Oaxaca, Mexico is described and illustrated. The species is distinctive by its panicles of spikes bearing elongate bracts and its tuberculate seeds that bear minute trichomes on the tubercles.

Rhynchosia diversifolia var. prostrata, sensu Grear (1978), is elevated to specific status where it is given a new name, Rhynchosia bicentrica, nom. and stat. nov., there being an earlier R. prostrata. Reasons for the elevation are provided, along with maps showing its amphitropical distribution.

Some historical considerations concerning the identity of Wissadula stellata (Cav.) K. Schum., lectotypifications of Sida stellata Cav. and W. fuscorosea Ulbr., the description of two new species (W. ecuadoriensis and W. macrocarpa), and the discussion of the legitimacy of a name widely but incorrectly used in Wissadula Medik., W. macrantha R.E.Fr., nom. illegit., are presented.

Four new species of the genus Aloysia are described: A. arequipensis, A. coalcomana, A. cordata, and A. velutina. A key to the species and a brief discussion of each novelty is included along with a key to the New World genera of the tribe Lantaneae.

The widespread Neotropical species Polygala glochidiata has traditionally been considered the only Polygala with uncinate seed hairs to occur in Mexico. A second species with such hairs is shown to occur partly sympatrically with P. glochidiata in Jalisco and Nayarit and is referred to P. minima, heretofore considered to be a species restricted to southern Brazil, Paraguay, and northern Argentina. A single collection from the state of México is also referred to P. minima, while the situation from Oaxaca southeastward into Central America is more complex. Patterns of variation in the P. glochidiata complex require further study, but data are presented to dispute the synonymization of P. minima into P. glochidiata by Bernardi.

A new arborescent species of Croton with accrescent pistillate calyx, Croton pascualii, is described and illustrated from the Pacific Slope of Oaxaca, Mexico. It has certain characteristics in common with Croton oerstedianus, a species included in the section Corylocroton. The proposed new species is characterized by its unisexual cymules, large and broadly ovate imbricate sepals of the pistillate flowers, and capsules ca 12 mm long. The foliage and resin of the new species have a pleasant, persistent aromatic fragrance suggestive of Quararibea or of celery (Apium graveolens). Croton pascualii is thus far known only from the Tropical Moist Semi-Evergreen Forest (selva mediana subperennifolia) of the Pacific Slope of Oaxaca, and has been collected in flower from June to September.