California bur-clover M. polymorpha var. vulgaris (Benth.) Shinners
Spotted bur-clover M. arabica (L.) Huds.
Source: Magness et al. 1971
The bur-clovers are so-called because the seed pods are spiny and coiled. The two species listed are of importance in the United States. Both are annuals native to the Mediterranean Area that became established in this country by chance. They are adapted only to areas where winter temperatures do not go much below freezing. California bur-clover is found mainly in the far west while spotted bur-clover is found in the Southeast. Although annuals, they commonly reseed, starting growth in the fall and furnishing winter and early summer pasture under mild conditions. Stems are rather weak, usually semiprostrate unless supported. Leaves are trifoliate with 3-heart-shaped leaflets. The bur-clovers combine well with grasses as pasturage. While nutritious, either as hay or pasture, they are less palatable to livestock than alfalfa or most other clovers. They are valuable as green-manure crops, especially in orchards where volunteer growth can be maintained if plants are allowed to mature a seed crop at intervals before turning under.