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1 Calyx strigose, the hairs neither spreading nor uncinate; [mostly of moist to wet habitats].
..2 Corolla limb 2-5 mm wide; mericarps taller than the style; stems terete; plant not stoloniferous; calyx usually deciduous in fruit, the lobes ≥ as long as the tube
..2 Corolla limb 5-10 mm wide; mericarps not surpassing the style; stems angled; plant often stoloniferous; calyx usually persistent in fruit, the lobes ≤ as long as the tube
....3 Corolla limb 1-4 mm wide; annual or biennial.
......4 Calyx lobes unequal, 3 lobes shorter than the other 2; corolla white; [native, of dry or moist habitats].
........5 Fruiting pedicels divergent; fruiting calyx deciduous, 3-10 mm long; inflorescence internodes usually longer than 10 mm; mericarps 1.4-2.2 mm long
........5 Fruiting pedicels more-or-less erect; fruiting calyx persistent, 3-5.5 mm long; inflorescence internodes usually shorter than 10 mm; mericarps 1.2-1.5 mm long