A systematic study of Boerhavia L. and Commicarpus Standl. (Nyctaginaceae) in Southern Africa
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The Nyctaginaceae Juss. is a small flowering plant family of about 30 genera and 400 species mainly found in the tropical and subtropical regions of the New World. In Africa, six genera and 49 species occur, and in southern Africa, five genera and 19 species. Boerhavia L. and Commicarpus Standl. are the most species rich genera in southern Africa, with seven and eight species respectively. These species have not previously been studied taxonomically nor phylogenetically, and the objective of this study was to provide a systematic and phylogenetic treatment of these groups for southern Africa. Plant material was collected from the diversity centres of Boerhavia and Commicarpus in southern Africa. Leaves, flowers and anthocarps stored in ethanol were measured and examined with a stereomicroscope and surface studies conducted with a scanning electron microscope (SEM). Material fixed in paraformaldehyde was embedded, sectioned, stained and examined with a light microscope. Pollen samples were acetolized before examination with a SEM. Sequencing analyses were done with a DNA Sequencer and neighbor-joining and maximum likelihood trees drawn. Distribution and habitat information were obtained from voucher specimens from various herbaria. The pollen grains are uniform in shape and sculpture and provide no diagnostic characters with which to distinguish between species. They do, however, provide broad characters to distinguish between the genera. Morphological, anatomical and molecular investigations, however, provided a series of characters to distinctly discern between Boerhavia and Commicarpus. Morphologically, Boerhavia and Commicarpus differ in growth form, inflorescence type, shape and indumentum of the upper and lower part of the flower, and shape and indumentum of the anthocarp. Anatomically, Boerhavia can be distinguished from Commicarpus by the Kranz anatomy around the minor veins of the leaves (which is absent in Commicarpus) and the sclerenchyma bundles which are present within the rib and inter-rib areas of the anthocarp (sclerenchyma bundles are only present in the rib area in Commicarpus). Molecular analyses group Boerhavia and Commicarpus as distinct clades with high bootstrap support. The differentiation is such in southern Africa, that Mirabilis and Acleisanthes, two non-African genera, are even placed intermediately between the two. The different species of Boerhavia and Commicarpus can be distinguished by the lower, coriaceous part of the flower and the anthocarp, as the arrangement of the glands, ribs and trichomes on these structures is species specific. The anatomy of the stems, leaves and anthocarps of the different species is uniform and uninformative and cannot be used to distinguish between the species. Molecular analyses support the distinction of the different species as defined by the morphology, and group the morphologically similar C. fruticosus and C. squarrosus in close relation. The aliens, Boerhavia cordobensis, B. diffusa var. diffusa and B. erecta, group together and the indigenous B. coccinea var. coccinea, B. deserticola, B. hereroensis and B. repens subsp. repens group together. The widely distributed C. plumbagineus and C. helenae var. helenae are closely related to each other, as are C. pentandrus and C. decipiens which are limited in theitr distribution to the African. This systematic study has shown that Boerhavia and Commicarpus are two distinct genera in southern Africa with well-defined species. This provides a workable classification system for southern Africa. This classification requires to be further refined by combining the morphology, anatomy, palynology and phylogenetics of the southern African Boerhavia and Commicarpus species into a single phylogeny. The phylogenetic investigations are, however, incomplete as the molecular analyses still need refinement and incorporation of more genes and taxa.