Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Genus Description - Sep persistent under the fr; ovary 10-locellar; style accrescent and forming a columnar beak at maturity; fr separating into 10 1-seeded, half-carpellary mericarps, these tuberculate on the back; germination epigeal; diffusely branched, prostrate to ascending herbs allied to Tribulus. 17, New World, mainly trop. and subtrop.