Rhododendron sect. Pentanthera G. Don (Ericaceae) comprises a group of closely related, highly ornamental plants which are commonly called ‘azaleas'. Thirteen of the fifteen species recognized in this section are indigenous to North America. One species (R. molle) is native to Japan and China, and one species (R. luteum) is indigenous to the Caucasus region. Phylogenetic analysis of the species within the section indicates that R. molle is the sister to the rest of the section. It is the sole member of R. subsect. Sinensia. The remaining species form a monophyletic group recognized as R. subsect. Pentanthera. Within this subsection the presence of a blotch on the upper corolla lobe defines two primarily orange to red-flowered groups. The first group has a Tertiary Period disjunct distribution and comprises R. luteum, R. austrinum and R. occidentale. The second group is indigenous to eastern North America and comprises R. calendulaceum, R. cumberlandense, R. flammeum, R. prunifolium and R. alabamense. In both groups the cladistically basal species has white flowers with a yellow blotch on the upper corolla lobe (R. occidentale, R. alabamense, respectively). The pink to white early flowering species R. canescens, R. periclymenoides and R. prinophyllum do not form a monophyletic group.

Phenetic analyses indicate that the eastern Asian taxon, R. molle, is best recognized as one species with two geographical subspecies; Rhododendron prinophyllum is quite distinct from R. canescens and R. periclymenoides. The latter two species are very similar morphologically, but their similarities are due to the retention of primitive characters and they should be recognized as distinct species. Rhododendron calendulaceum can be distinguished from R. cumberlandense using a combination of morphological and phenological characters. The various taxa previously segregated out of R. viscosum are merely extreme forms of a widespread and variable species and are not given any formal rank. No subspecific taxa are recognized for R. occidentale. Distribution maps, keys to the species, species descriptions and specimen citations are included.

Chromosome numbers for 11 genera and 36 species in the predominantly South African tribe Manuleae (Scrophulariaceae) are presented, the majority being first reports. The basic numbers of the genera form a dysploid series, x = 6, 7, 8, 9. The somatic number of most of the species is diploid, ranging from 2n = 12 to 2n = 18; that of Jamesbrittenia, 2n = 24, is probably of polyploid derivation. The highest somatic number encountered in this survey is that in Camptoloma lyperiiflorum, with 2n = c.56, which, taken in conjunction with a published count of 2n = 28 for another species of Camptoloma, is octoploid based on x = 7. This is the only example, so far, of intrageneric polyploidy in the Manuleae. The somatic number in certain genera appears to be constant over some subgeneric divisions (e.g. Jamesbrittenia, 2n = 24), but variable in others (e.g. Sutera, 2n = 12, 14). The variation in chromosome number observed in this study parallels and corroborates the redefinition of generic boundaries proposed by O. M. Hilliard. One species of Selago (in the tribe Selagineae) was also included in this survey for cytological comparison with Tetraselago (Manuleae).