Some 250 species of Trifolium are recognized throughout the world, with about 50 indigenous in the United States. None of these native species are cultivated although they contribute to grazing and may be an important part of wild hay crops. They contribute nitrogen and thus promote the growth of associated grass. The clovers may be annual or perennial. Leaves are mostly trifoliate, rarely 5 to 7 leaflets. Flower heads are usually short spikes or umbels with numerous small individual flowers in the head. The important agricultural species are described as follows:
Trifolium pratense Handbook of Energy Crops. James A. Duke. 1983. unpublished.
Red Clover Magness, J.R., G.M. Markle, C.C. Compton. 1971. Food and feed Crops of the United States.
FactSHEET on T. ambiguum Kura clover contributed by: Norman L. Taylor
T. agrarium, T. campestre, T. dubium - Hop clovers
T. fragiferum - Strawberry clover
T. glomeratum , T. lappaceum - Cluster clover, Lappa clover
T. hybridum - Alsike clover Swedish clover
T. incarnatum - Crimson clover, Italian or Scarlet clover
T. michelianum - Bigflower clover
T. resupinatum - Persian clover
T. variegatum - Whitetip clover
T. willdenovii - Seaside clover