Senna obtusifolia

Author: (Linnaeus) Irwin & Barneby

Morphological description
Herb or undershrub up to 1 m tall, rarely higher (2.5 m), usually foetid smelling, glabrous or thinly pubescent. Stipules setaceous, 10-15 mm, caducous.

Leaves paripinnate with 3 pairs of leafletls. petiole 1-4 cm; rachis 2-3 cm, with a subulate, 2 mm long gland between the lowest pair of leaflets. Leaflets obovate, shortly petiolulate; membranous, 1-6 by 0.5-4 cm, increasing in size distally, apex rounded and mucronate, base cuneate.

Inflorescence: Racemes axillary, 1- or 2(or 3)-flowered on a very short peduncle; bracts linear, acute; bracteoles absent;pedicels 1.5-3.5 cm long, elongating to 2-4.5 cm in fruit.

Flower: Sepals 5, subequal, ovate, 5 by 2-4 mm. Petals 5, yellow-orange, unequal, short-clawed, 1-2 cm long. Stamens 7, nearly equal, filaments 1.5-2 mm, anthers 3 longer, 4 smaller 1.5-2.5 mm, opening by apical pores, the three larger anthers narrowed shortly below the apex like a bottleneck; staminodes 0-3; filaments of all stamens straight.

Pods linear, terete, falcate to straight, 13-23 by 0.4-0.7 cm.

Seeds 20-30, ovoid-rhomboid, 5-6 by 2-4 mm with very narrow areoles 3-4.5 by 0.3-0.5 mm.

Origin uncertain, spread throughout the tropics. It is rare in the Malesian area. It has been collected from Singapore, Java, the Philippines and New Guinea, but probably occurs all over.

In the Malesian area only at low altitudes.

1. This species is so closely related to Senna tora that several authors have regarded them as conspecific, e. g. Bentham. They are, however, two clearly separated taxa best kept at species level; this was elegantly demonstrated by Brenan (1958: 248). The strong foetid smell of S. tora is usually absent from S. obtusifolia which is also recognizable by the much longer pedicels and by the differences in the areole. The singular foliar gland is mostly a good character; it is, however, pointed out by several authors that particularly in Africa a 'race' with two foliar glands has been introduced and spread. Generally S. obtusifolia is readily recognizable even in the field by the longer pedicels.
2. Concerning the typification that of Brenan (1958: 248) clearly overrules that of de Wit (1956: 254).