Creeping indigo (Indigofera spicata Forssk. and Indigofera hendecaphylla Jacq.) is a perennial legume grown in tropical and subtropical regions mostly as a cover crop and for green manure. Highly palatable and nutrient-rich, it was once considered as a potentially valuable fodder but the toxicity of certain varieties for all livestock species led to its abandonment. Creeping indigo is still used for pasture in East Africa.
Creeping indigo has a creeping or weakly ascending habit. Its stems, arising from a central basal crown, can be 1 m long and grow to a height of 0.5 m. Creeping indigo has a deep woody taproot. Its stems are green, pubescent and somewhat flattened when young, and become brown in colour when they get older. The leaves are alternate and pinnately compound, 12-40 mm long, with alternately arranged leaflets that are dull green at their upper surface. The inflorescences are arranged in erect, spike-like racemes, salmon pink to red-orange in colour. The flowers are papillionaceous, 3-4 mm long. The fruits are linear-oblong pods, 10-18 mm long x 1.5-2 mm wide, borne in dense descending clusters. They are dehiscent and contain 4-8 cuboid, smooth seeds (Cook et al., 2005; Du Puy et al., 1993). Indigofera spicata and Indigofera hendecaphylla were considered to be the same species until 1993 and are morphologically close, though Indigofera spicata has shorter pods and inflorescences, and a lower number of leaflets per leaf (Du Puy et al., 1993).
Creeping indigo is mainly planted as green manure and as a cover crop in coffee, tea or rubber plantations. It is very palatable to livestock (except pigs) and has been reported to be used for fodder in East Africa and India. Indigofera spicata was mentioned as a pasture species in Ethiopia as recently as 2014 (Bezabih et al., 2014). It was once considered to be a promising fodder able to form well-balanced mixtures with grasses. However, in the 1940-1950s, feeding trials and field observations in the USA demonstrated that the plant was toxic for cattle, sheep, rabbits, pigs, Guinea pigs, horses and chicks, so attempts to use it as fodder were abandoned (see Potential constraints on the "Nutritional aspects" tab) (Emmel et al., 1941; Freyre et al., 1952; Nordfeldt et al., 1952; Morris et al., 1954; Morton, 1989). There is also a report that the plant was once used for forage in East Africa and then abandoned after it was found to be toxic (Morton, 1989). In Australia, creeping indigo was imported as potential pasture legume but rejected for this purpose after its toxicity was recognised (Aylward et al., 1987). Creeping indigo used to be a source of dye but is now replaced by synthetic dyes (Sunarno, 1997; Duke, 1981).
Due to the confusion between Indigofera spicata and Indigofera hendecaphylla in pre-1993 studies, properties once attributed to Indigofera spicata, notably its toxicity and invasiveness, may actually concern only Indigofera hendecaphylla (Sunarno, 1997). At the time of writing (December 2014), such differences are far from clear due to the lack of recent literature. It may be possible that African strains of Indigofera spicata, which are still used for fodder in their native range, are valuable fodder and would deserve attention (Sunarno, 1997), but Indigofera spicata plants have been considered toxic to livestock in Australia (Ossedryver et al., 2013).