This ranges widely across central and eastern states, but it is concentrated on dry sandy soils of the Great Plains, midwest and coastal regions. In Ky. it is known only from sandy banks of the Ohio Rv. in BALL (EKY, WKY), and the Mississippi Rv. in FULT (JC for KY). Triplasis (2n = 40) is a small genus closely allied with Tridens (2n = 40 in most species).