A Revision of the African Species of Sesbania

T h e present paper is an attem pt to revise the African species of the genus Sesbania, family Papilionaceae. Imperfect as it may prove to be, it is long overdue, chiefly because of the great accumulation of herbarium material since the publication of the second volume of the “ Flora of Tropical Africa ” in 1871, much of this material having remained unnamed or imperfectly determined. The results of this investigation might very well have been more satisfactory to the authors had there been more field notes available regarding the situation, habit, floral colouring, etc., of the specimens accumulated in the various herbaria which they have been able to consult.* That this information is vital in the determination and limitation of the species of Sesbania, a t least, has been well demonstrated by Prain f in his critical elucidation of the Indian species. The genus Sesbania contains about fifty species which occur in the warmer parts of the world, mainly in or by the sides of streams, lakes, and swamps. I t appears to attain its greatest development in tropical Africa, a few of the species extending into South Africa as far as Natal, and into various parts of the Transvaal and Bechuanaland. In the present revision of the species from this area twenty-three are recognized to be distinct. They belong to two sections, nineteen to Eusesbania and four to Daubentonia, the latter characterized by its four-winged fruits. The third and purely American section into which Sesbania was divided by Bentham and Hooker (Gen. PI., I, 502) is now recognized by American botanists J as a distinct genus, Glottidium, and the present authors’ views coincide in respect to this. They cannot, however, go so far as to accept the American view regarding the generic status of Daubentonia which occurs in the three widely separated areas, namely, the south-eastern United States and Mexico, sub-tropical South America; and tropical East Africa. This broken distribution seems to point to a separate origin of the species of Daubentonia from the basal stock, Eusesbania, species of which occur in all these areas. Glottidium, on the other hand, a native of Florida, is well separated from Sesbania by its short fruits with only two seeds and the manner of dehiscence, the seeds remaining inside the dry bladder-like endocarp which detaches itself as a whole from the outer shell. In the case of the African species we have found a most useful and constant character in the nature of the appendages on the claw of the vexillum. In the first five species shown in the key these are long and quite free from the vexillum in their upper half. In