Vernonieae (Asteraceae) of southern Africa: A generic disposition of the species and a study of their pollen.

Current and previously included members of the Tribe Vernonieae (Asteraceae) of southern Africa are listed in their presently recognized genera with complete synonymies and keys to genera and species. The genus Vernonia, as presently delimited, does not occur in Africa. Genera of the Vernonieae presently recognized from southern Africa are Baccharoides, Bothriocline, Cyanthillium, Distephanus, Erlangea, Ethulia, Gymnanthemum, Hilliardiella, Oocephala, Orbivestus, Parapolydora, Polydora, Vernonella, Vernoniastrum, plus two genera that are named as new: Namibithamnus and Pseudopegolettia.

Two new genera, Hoffmannanthus and Jeffreycia, mostly from East Africa (Erlangeinae, Vernonieae, Asteraceae).

Two genera of Vernonieae subtribe Erlangeinae with Type A pollen, 5-ribbed achenes, and blunt-tipped sweeping hairs on the styles are described as new, Hoffmannanthus with one species and with Vernonia brachycalyx O. Hoffm. as type, and Jeffreycia with five known species, with Vernonia zanzibarensis Less.

Pantoporate pollen in the Asteraceae (Vernonieae).

Pantoporate pollen, which occurs sporadically in the Monocots and Dicots, has now been found in Asteraceae in two apparently related genera of the tribe Vernonieae, Polydora Fenzl and Oocephala H.Rob. Disposition of pores in Polydora seems more asymmetric than in Oocephala.

Lettowia, a new genus of Vernonieae from East Africa (Asteraceae).

A new genus, Lettowia H. Rob. & Skvarla is named for the single East African species originally described as Vernonia nyassae Oliv.

Pollen wall development in flowering plants.

The outer pollen wall, or exine, is more structurally complex than any other plant cell wall, comprising several distinct layers, each with its own organizational pattern. Since elucidation of the basic events of pollen wall ontogeny using electron microscopy in the 1970s, knowledge of their developmental genetics has increased enormously. However, self-assembly processes that are not under direct genetic control also play an important role in pollen wall patterning.

Annulus-pore relationship in Gramineae (Poaceae) pollen: the pore margin of Pariana.

Pariana, a primitive bamboo, is the only genus in the Gramineae (Poaceae) to have pollen grains without an annulus as part of its single aperture (porate) system. In contrast, the markedly thickened exine layer underlying the pore margin is similar to counterparts in all grass genera. Components of the future annulus in Gramineae pollen develop toward the cytoplasm (proximally) and begin to be pressed outward by an increase in the cytoplasm during the microspore vacuolate stage, culminating in an annulus by maturity.

THE EVOLUTION OF POLLEN TETRADS IN ONAGRACEAE.

In Onagraceae, pollen is shed in mature tetrads in most Epilobieae, many species of Ludwigia (Jussiaeeae), and two closely related species of the large genus Camissonia (Onagreae). Mature tetrads of Camissonia cardiophylla and representative species of Epilobium and Ludwigia were examined with light, scanning, and transmission electron microscopes. Morphological diagnoses of monad units indicated that individual taxa could be readily distinguished.