This is widespread in western North America and Central America, with a notable concentration in the central Great Plains but also extending into some midwestern lowlands (Cusick 1989; K). It grows mostly in shallow ponds, shorelines and mudflats that dry gradually during the summer. It has often been confused with coccinea, and further study is needed for reliable separation of records (Graham 1985; Cr). A. robusta differs in its pale lavender petals (versus rose-purple) and pale yellow anthers (versus deep yellow); shorter peduncles (0-1 mm versus 0-4+ mm) and pedicels. Its fruits tend to be larger (4-6 mm thick versus 3.5-5 mm) and less numerous per axil (usually 1-3 versus 3-5). Its leaves tend to be relatively large on well-grown plants (up to ca. 50-70 x 5-10 mm), but those on branches and smaller plants are more like coccinea (mostly ca. 20-40 x 3-5 mm).