Pongamia

Pongamia is a genus of legume in the Fabaceae family. Recently it has been proposed that the genus Pongamia be rejected in favor of the genus Millettia, and many species have been reclassified. Due to recent interest in biofuels, pongamia is often the generic name given for Millettia pinnata, a tree being explored for producing biodiesel. In 1834, Robert Wight and George Arnott Walker-Arnott, both Scottish botanists, published Prodromus Florae Peninsulae Indiae Orientalis where they describe pongamia (growing in British gardens as an introduced species) as: 'Calyx cup-shaped somewhat truncated and 5-toothed. Corolla papilionaceous glabrous. Stamens at first diadelphous at the base and apex and monadelphons about the middle, afterwards usually entirely diadelphous. Legume more or less compressed, more or less oval, with a short recurved point, 1-celled (neither contracted nor with partitions between the seeds), 1-2 seeded: valves concave on the inside, not separating naturally. Trees or twining shrubs. Leaves unequally pinnated: leaflets opposite.' A more modern description describes Millettia pinnata as a medium-sized evergreen or briefly deciduous, glabrous shrub or tree 15–25 m high, with straight or crooked trunk 50–80 cm or more in diameter and broad crown of spreading or drooping branches. Bark grey-brown, smooth or faintly vertically fissured. Branchlets hairless with pale stipule scars. Leaves alternate, imparipinnate with long slender leafstalk, hairless, pinkish-red when young, glossy dark green above and dull green with prominent veins beneath when mature. Leaflets 5-9, paired except at end, short-stalked, ovate elliptical or oblong, 5-25 x 2.5–15 cm, obtuse- acuminate at apex, rounded to cuneate at base, not toothed at the edges, slightly thickened. Inflorescence raceme-like, axillary, 6–27 cm long, bearing pairs of strongly fragrant flowers; calyx campanulate, 4–5 mm long, truncate, finely pubescent. Flower clusters at base of and shorter than leaves, to 15 cm long, slender, drooping. Flowers 2-4 together, short-stalked, pea-shaped, 15–18 mm long. Calyx campanulate, 4–5 mm long, truncate, finely pubescent; corolla white to pink, purple inside, brownish veined outside, 5- toothed, standard rounded obovate 1–2 cm long, with basal auricles, often with green central blotch and thin silky hairs on back; wings oblong, oblique, slightly adherent to obtuse keel.