Stems 2-10 dm, freely branched when well developed, the branching tending to begin at the base, with the lowest pair of branches initially decumbent and often nearly as long as the main stem; lvs rather thick and fleshy, linear or narrowly oblong, to 10 נ1.5 cm, usually much smaller, ±clasping at the truncate or auriculate, often dilated base; fls 1-3 per axil, virtually sessile, the stout peduncle and pedicels to ca 1 mm, or wanting; fls a little larger than in no. 1, the hypanthium mostly 2.5-4.5 mm at anthesis, the caducous pet 2-3+ mm, pale lavender in life; anthers 4 or 8, light yellow; hypanthium about equaling and largely enclosing the fr, but open at the top, ovary and fruit 4-locular; the persistent style 1.5-3 mm, exserted; fr globose, 3.5-5+ mm thick; 2n=34. Edges of ponds, grassy swales, and similar wet places; N.J.; O. to N.D. and Wash., s. to C. Amer. July-Sept. Often confused with no. 2 [Ammannia coccinea Rottb.] in the past.
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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Indiana Coefficient of Conservatism: C = 2
Wetland Indicator Status: OBL
Diagnostic Traits: Similar to but more rare than A. coccinea. The flowers in A. robusta are sessile while of A. coccinea have peduncles to 4.5 mm long.
Citation: The vPlants Project. vPlants: A Virtual Herbarium of the Chicago Region. http://www.vplants.org
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