trefoil trēˈfoil [key] [O.Fr.,=three-leaf], in botany, name for several plants, chiefly of the pulse family, having trifoliate leaves. Best known of the trefoils is clover. The bird's-foot trefoil (Lotus corniculatus) is an Old World forage plant and weed that has been naturalized in North America; the prairie trefoil (L. americanus) is a related native American plant. The shrubby trefoil is the hop tree. Tick trefoil is a name for the tickseed, or beggarweed.

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