Trifolium

The clover genus Trifolium has 250-300 species (Allen and Allen 1981; Zohary and Heller 1984; Ellison et al. 2006), about 10% (20-30) of which are used as forage plants in commercial agriculture, and a greater number are used locally for fodder in their native zones. This chapter will give most consideration to the wild relatives of the most important of these species, white clover (T. repens L.), red clover (T. pratense L.), and berseem (T. alexandrinum L.). However, there are nearly 50 other species, which are listed here as being of current or potential interest, either for direct use in agriculture, or as sources of genes for other species. Clovers, like most legumes, are co-evolved complexes of plant, symbiotic bacteria, fungi, and insect pollinators. Strains of symbiotic N-fixing bacteria (Rhizobium leguminosarum biovar trifolii) have co-evolved with plant species and populations, and form an important part of the species adaptations. These are mentioned, but have not been comprehensively reviewed. Similarly, pollination and mycorrhizal associations are indicated only where they are of special significance. We have based our classification of species relatedness on the DNA phylogenetic analysis of Ellison et al. (2006), which replaces the former morphological classification of Zohary and Heller (1984).