Clover

The Leguminosae is one of the largest families of flowering plants, comprising more than 650 genera and 18,000 species (Polhill and Raven 1981). Legumes are second to cereal crops in agricultural importance, based on area harvested and total production. One of the most important attributes of legumes is their unique capacity for symbiotic nitrogen fixation, underlying their importance as a source of nitrogen in both natural and agricultural ecosystems. Seeds of legumes provide about one-third of all dietary nitrogen derived from protein and one-third of processed vegetable oil for human consumption (Graham and Vance 2003). Legumes are also sources for many natural products (secondary metabolites), such as lignins, flavones, flavonols, methoxyflavonols, coumestans, isoflavans, anthocyanins and proanthocyanidins (condensed tannins). Most of these metabolites play important biological roles in plants, including the attraction of pollinators and agent~ of seed dispersal to flowers and fruit by visual cues, pollen development, signalling associated with plantmicrobe interactions, and protection from ultraviolet light, herbivores and pathogens. In addition to their importance as sources of dietary protein for humans and animals, legumes provide health-related natural products including dietary fibre, hormone analogues and anti-oxidants (Dixon and Sumner 2003)