Sesbania sudanica J.B.Gillett

Bidgood, S. & Friis, I. 2009. Reconsideration of the African species Sesbania sudanica and S. hepperi (Leguminosae subfam. Papilionoideae) as to their variation in Ethiopia. Kew Bulletin 64: 301. DOI: https://doi.org/10.1007/s12225-009-9119-1

Type

Sudan, Gedaref Distr., near Sugara, 25 Sept. 1951, Beshir 135 (holotype K!).

Note

S. sudanica subsp. occidentalis J. B. Gillett (1963: 136), synon. nov. Type: 58 – 64 km E of Accra on road to Ada, 18 March 1960, Akpabla 2036 (holotype K!; isotype GC). S. hepperi J. B. Gillett (1963: 137), synon. nov. Type: Nigeria, Adamawa province, between Yola and Jimeta, 190 m, 1 Nov. 1957, Hepper 1196 (holotype K!). In J. B. Gillett’s revision of Sesbania (Gillett 1963) and in the floras based on the taxonomy of that revision there is a large group of annual savanna species of Sesbanialacking, or having very short free tips on the appendages of the standard. The characters distinguishing between these species are mainly quantitative and some are very slight, and the species have proven to be quite difficult to define and identify. We have produced a table of characters (Table 1) of what we find are the taxa most clearly related to our Ethiopian material, including S. sudanica, S. sudanica subsp. occidentalis, S. hepperi, S. dalziellii E. Phillips & Hutch., S. greenwayi J. B. Gillett, S. paucisemina J. B. Gillett, S. microphylla E. Phillips & Hutch. and S. leptocarpa DC. The information in Table 1 is as far as possible based on information in Gillett’s revision or his account of the genus for the Flora of Tropical East Africa, but because his revision did not give full descriptions of already established species it has in a few cases been necessary to supplement this with information from specimens named by him at K. It appears from the comparison that our plants, together with S. hepperi, S. sudanica, and S. sudanica subsp. occidentalis, can be distinguished from other species without free tips on the appendages of the standard by the following characters: style pilose, pubescent or tomentose (although the style of S. greenwayi is pubscent in the upper part), rostrum 10 – 15 mm long and pods not or only faintly torulose.

Morphology General Habit

Annual herb with glabrous (rarely slightly pubescent in the youngest parts), slightly glaucous and striate stems that may be softly woody at the base, up to c. 3, rarely 5 m high (one specimen has been described as prostrate); stems up to 20 mm in diameter, unbranched or very little branched

Morphology Leaves

Leaves spirally arranged. Stipules linear-lanceolate, erect, 4 – 5 mm long, glabrous, very soon falling and leaving a linear scar

Morphology Leaves Petiole

Petiole 1 – 2 cm long, with a brownish coloured joint (pulvinus), at base

Morphology Leaves Rachis

Rachis 12 – 20 (– 25) cm long, not aculeate

Morphology Leaves Leaflets

Leaflets in (10 –) 20 – 40 (– 50) pairs, gradually decreasing in size towards the tip, glabrous, oblong with parallel sides, very variable in size from being small near the top of the plant to much larger on the lower parts of the stems, with an interval of 3 – 5 mm between the leaflets, petiolules up to c. 0.5 mm long, lamina of leaflets 5 – 22 × 1.5 – 4 mm, green above, greyish-green below, apiculate

Morphology Reproductive morphology Inflorescences

Racemes with 4 – 10 (– 15) flowers; peduncle 1 – 2.5 (– 3) cm long, glabrescent; rachis 5 – 20 (– 30) cm long, including peduncle, prolonged in fruit, but only the 2 – 3 lowermost flowers normally develop fruits

Morphology Reproductive morphology Flowers Pedicel

Pedicels 5 – 12 mm long, very thin, up to 15 mm in fruit, thickened; bracts and bracteoles linear, 1 – 2 mm long, bracts inserted near the middle of the pedicel, caducous, bracteoles inserted just below the receptacle, not falling as early as the bracts. Receptacle glabrous, 1 – 1.5 mm long; calyx tube 3 – 5 mm long, broadly campanulate to almost cylindrical; calyx teeth triangular, 1 – 2 mm long, faintly tomentose along the margin

Morphology Reproductive morphology Flowers Corolla

Standard with lamina almost circular in outline, 15 – 18 × 15 – 18 mm, standard appendages at base less than 1 mm wide, with no free tips or free tips less than 0.5 mm long; claw c. 5 mm long. Wings with oblong lamina, 15 – 18 × 4 – 7 mm, with apiculate basal projection 1 – 1.7 mm long; claw 3 – 5 mm long Keel with broadly ovoid lamina, 7 – 10 × 5 – 6 mm, with hooked apiculate projection at base 1 – 3 mm long; claw 8 – 9 mm long Corolla yellow, with dark purplish brown spots on outside of standard and wings

Morphology Reproductive morphology Flowers Androecium Stamens Filaments

Filament tube 12 – 16 (– 20) mm long, free part of filament 3 – 6 mm long

Morphology Reproductive morphology Flowers Gynoecium Ovary

Ovary with 30 – 45 ovules, glabrous, 14 – 18 mm long; style pubescent or at least with a few hairs in the upper part, 5 – 6 mm long

Morphology Reproductive morphology Fruits

Ripe pod with 20 – 30 (– 40) seeds, unwinged, but with a thickened suture c. 1 – 2 mm broad, 22 – 28 cm long, including the 10 – 15 mm long apical beak and the 10 – 15 mm long basal stipe without developed seeds, 2 – 3 mm thick, septae (5 –) 6 – 8 mm apart

Morphology Reproductive morphology Seeds

Seeds brown, hardly maculate, rounded to subcylindrical, 3 – 4 × c. 1.7 × 1.4 mm; hilum c. 1.2 mm from micropyle.

Distribution

Ethiopia, Sudan, Central African Republic, Cameroon, Nigeria, Togo, Burkina Faso, Ghana, Mali, Gunea.

Ecology

Our field observations in western Ethiopia indicate that specimens of Sesbaniasudanica are found in depressions with black cotton soil where the dominant surrounding vegetation is Terminalia-Combretum woodland. Sometimes the plants grow up through thorny thicket, e.g. of Dichrostachys cinerea, but they may also occur in open grassland on black cotton soil and in other habitats that remain damp for a long time, e.g. in road ditches and in damp places in dry river beds. This agrees well with label information from Sudan, where the species has been recorded from depressions dominated by Oryza spp. in broadleaved woodland, in swampy places in grassland, and on heavy clay soil. Among the more incomplete habitat notes recorded on labels from West Africa are stream beds, swampy areas in woodlands or dried up swampy areas by roadsides. The recorded altitudinal range is 150 – 750 m a.s.l.

Conservation

With a distribution almost from the Atlantic to the Ethiopian Highlands it seems that Sesbaniasudanica should be placed in the IUCN category of Least Concern (LC).