Apium leptophyllum (Pers.) F.Muell.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Three other spp. are merely casual with us. A. leptophyllum (Pers.) F. Muell., of trop. and subtrop. Amer., is an annual with filiform lf-segments. A. repens (Jacq.) Lag. and A. nodiflorum (L.) Lag. are Mediterranean rhizomatous perennials. The former has a well developed involucre, the latter does not.