Siamese senna (Senna siamea (Lam.) H.S. Irwin & Barneby) is a medium-sized, fast-growing tree legume that is used as fodder and browse for ruminant livestock in tropical lowlands. Its fruits and pods are edible and its wood can be used for fuel or for making poles and furniture. Siamese senna provides many environmental services and is used as an ornamental.
Morphology
Senna siamea is an evergreen, medium-sized, many-branched tree legume. It reaches 10-12 m on average, rarely exceeding 20 m, and can exceptionnally reach 30 m (Rojas-Sandoval et al., 2013). Its root system consists in few thick and deep roots and in a dense mat of rootlets that spreads rapidly (up to 7 m in one year) (Orwa et al., 2009). Siamese senna is easily uprooted by strong winds (Rojas-Sandoval et al., 2013). The trunk is straight, up to 30 cm in diameter, with a rounded and dense crown. The bark is gray to light brown, becoming fissured with age (Orwa et al., 2009. The leaves are alternate, 10-35 cm long, pinnatelay compound with 6-14 pairs of leaflets. Leaflets are oblong in shape, 3-7 cm long x 1.2-2 cm broad, dark green in colour with a midrib ending in a short bristle (Orwa et al., 2009). The inflorescence is upright, borne on peduncles at the apex of the branches. It is a 30- 60 cm long x 13 cm broad panicle of bright yellow pentamerous flowers, 3 cm in diameter (Orwa et al., 2009). The pods are numerous, long, narrow, 5-25 cm long x 12-20 mm broad, flat, dark brown, dehiscent and compressed between seeds. The seeds are numerous (20-30), bean-shaped, shiny, dark brown, 8 mm long, with distinct areole (Orwa et al., 2009). There are 35,000 to 41,000 seeds per kg (Rojas-Sandoval et al., 2013).
Uses
Senna siamea is grown for fodder and browsed by livestock, though the extent of this use is unclear: it has be described both as occasional (Göhl, 1982) and widespread (Orwa et al., 2009). In any case, it should be used only for feeding ruminants, as its leaves, flowers and pods foliage contains alkaloids and anti-nutritional compounds that are toxic to non-ruminants such as pigs and poultry, which should be kept away from the plantations (Orwa et al., 2009). The limited information available seem to indicate that it can be used safely for rabbits (see the Rabbit section below). The fruits and leaves are used for food as vegetables or in curries but cooking water should be replaced 3 times to remove undesirable substances. Though it produces some smoke, the wood can be used as fuelwood or to make high grade charcoal. The timber makes hard to very hard wood that is resistant to termites. While difficult to work with, it used to make poles, posts, bridges, mine timbers and the heartwood for cabinet-making joinery and other decorative uses. All parts of the plant can be used for tanning. The concentrations of tannin vary from 17% in the leaves to 9% in the bark and 7% in the fruits. Siamese senna is used in China as a host plant for the lac insect. In India, it is used as a host for sandalwood (Santalum spp.), a parasitic tree producing the well-known aromatic (Orwa et al., 2009).
Senna siamea provides many environmental services. It is used to reforest denuded hills and mining sites, for shade and hedges, as windbreaks, and it is planted as an ornamental (Ecocrop, 2019). Siamese senna has been mentioned as a potential agroforestry species (Ecocrop, 2019).
