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....3 Epicalyx of 3 linear or linear to narrowly lanceolate bractlets; petals white or pink, 3-15 mm long; annual, sprawling, usually branched at the base (except M. verticillata).
......4 Bractlets of the epicalyx linear; petals to 3-5 mm long, white to pale lilac
......4 Bractlets of the epicalyx broadly linear to narrowly lanceolate; petals (3-) 5-15 mm long, pink or purple (rarely white).
........5 Stems erect, usually > 5 dm long; leaf blades 3-8 (-17) cm long, usually prominently crisped/puckered along the margin; flowers all or mostly sessile or subsessile
........5 Stems prostrate to ascending, to 5 dm long; leaf blades 1.5-5 cm long, planar; flowers (at anthesis) mostly on pedicels longer than the calyx.
..........6 Petals 6-13 mm long, about 2× as long as the sepals; mature mericarps slightly roughened or obscurely reticulate