Amphidiploid of nos. 1 [Ammannia auriculata Willd.] and 3 [Ammannia robusta Heer & Regel]; stems often freely branched; cymes mostly with 3 or more fls, subsessile or on a short stout peduncle to 4+ mm; pedicels short and stout, or none; hypanthium mostly 2-3.5 mm; pet 1.7-2.5+ mm, deep rose-purple; anthers deep yellow; fr 3.5-4.5 mm thick; 2n=66. N.J. and Pa. to N.D., s. to trop. Amer.; Calif. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.