Erect or prostrate, 1-4 dm, often freely branched; lvs opposite or whorled, linear-spatulate, 1-3(-5) cm, mostly obtuse; sep alternating with triangular appendages of nearly the same size; pet white or pink, minute, caducous; fr 3-5 mm; 2n=32. In mud or wet soil; near the coast from Mass. to Fla. and Tex.; inland from O. and Mich. to Minn., Ark., and Okla.; also on the Pacific coast, in Mexico, and trop. Amer.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
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From Flora of Indiana (1940) by Charles C. Deam
All the specimens [of the typical variety] are from the wet sandy areas of the northwestern part of the state. It is local and is found in ditches and on the borders of sloughs. My specimens of [var. interior, a form with wider leaves (5-10 mm wide) and larger capsules (mostly 3.8-4.4 mm wide,] are all from southern Indiana except a typical one from Steuben County. Infrequent to local and found in mud in ditches, on borders of sloughs, on muddy shores of streams and artificial ponds, and in wet woods and fallow fields.