Author: (Collad.) Irwin & Barneby
K. & S.S. Larsen in Fl. Camb., Laos & Vietn. 18 (1980) 102, pl. 17/4-5; in Fl. Thail. 4 (1984) 120, f. 29/4-5.
Morphological description
Large shrub or small tree , 2-6 m tall; young parts strigulose later glabrous. Stipules linear falcate, 6-15 mm long.
Leaves (sulfurea Senna Ic Blanco 426b )paripinnate with 4-6 pairs of leaflets; petiole 3-5.6 cm; rachis 5-15 cm with a clavate gland, 1-2 mm long, between the 2 or 3 (or 4) lower pairs of leaflets. Leaflets with short petiolule, broadly elliptic-lanceolate, 5-10 by 2-4 cm, with acute apex; upper surface glabrous, lower sparsely pubescent.
Inflorescences lateral racemes with peduncles 3-10 cm, axis 1-6 cm; bracts ovate acute, 3-8 mm long, finally reflexed; braceoles absent; pedicels 1-3 cm.
Flower: (sulfurea Senna fl Ic Blanco 426 )Sepals 5, green to reddish-brown, 2 outer suborbicular c. 3 mm, the 3 inner obovate, increasing to 6-9 mm in length. Petals 5, bright yellow (drying orange or pinkish-brown), ovate-obovate, 1.5-2 cm long, with a narrow claw 1-1.5 cm long. Stamens 10 fertile with straight, thick, short filaments, 1-4 mm; anthers subequal 5-7 mm long, opening apically by short slits. Ovary strigulose; style glabrous, filiform; stigma inconspicuous.
Pods flat, glossy, 12-17 by 1.5-1.8 cm with papery valves.
Seeds 20-30, oblong-elliptic, c. 7 by 4 mm.
Distribution
Native to India and Burma. Now also naturalized in the Neotropics.
Habitat
It seems to have a wide ecological amplitude. It is naturalized widely in the Indo-Malesian region in open, disturbed forests, waste places and around villages.
Uses
Cultivated as ornamental throughout SE Asia from remote times, also grown as a shade plant.
Notes
1. This species and Senna surattensis belong to sect. Psilorhegma (Vogel) Irwin & Barneby (1982: 77); a full account of the intricate nomenclature of these two taxa is given there.
2. Larsen & Ding Hou (1996: 688) do not maintain f. ferox de Wit, known only from two collections. It may be an ecotypical deviating form as suggested by the author.