A taxonomic revision of the genus Sesbania (Fabaceae: Sesbanieae) in southern Africa, including introduced species

• Sesbania is revised for the Flora of southern Africa region. • Sixteen taxa are recognised. • Three taxa are alien and are included in the revision. • Sesbania tetraptera is treated as a member of sect. Sesbania rather than sect. Daubentonia. The genus Sesbania (Fabaceae) comprises approximately 80 species distributed in tropical and subtropical regions. Species circumscription of southern African members of Sesbania has been problematic due to overlapping morphological variation and had not been updated since a revision in 1963. Many specimens in various herbaria remained misidentified or identified only to genus level. The aims of this study were to conduct a detailed taxonomic revision of Sesbania (native and introduced species) in southern Africa and to identify characters that reliably distinguish species. Data were mainly obtained from herbarium specimens and were augmented with some populations in the field, various online resources and plant databases. Measurements were mainly on herbarium specimens, using a microscope for smaller features. Distributions were recorded as Quarter Degree Squares and maps were prepared using centroids. Where sufficient distribution data were available, Extent of Occurrence and Area of Occupancy were calculated with GeoCAT. Recommendations for threat status considering the latest IUCN criteria are provided. Two sections are recognized (viz. sect. Sesbania and sect. Daubentonia ) with the major delimiting characters being the presenceof a rim-aril on the seed, the presence of teeth on the base of the keel petal blade and seed shape. Sixteen taxa (including three alien) are recognized with major delimiting characters between species being colour of the standard, presence of standard petal appendages, attachment of the standard petal appendage tip, keel shape, presence of hairs on the style, wings on the pod, pod length, seed length, colour of seed testa, seed shape and presence of a rim-aril. A comprehensive taxonomic treatment of Sesbania in southern Africa is presented with an identification key. Nomenclature (with synonyms), a description, distribution data, ecology, phenology, etymology and conservation status are included for each taxon.