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1 Flowers on pedicels 1-5 mm long, with bracteoles near the base of the pedicel; inflorescences umbel-like, leaf-opposed or terminal, on peduncles 1-12 mm long; capsules 7-14 mm across; [section Pyramis].
..2 Leaf blades glabrous or nearly so, the hairs simple (if present); inflorescences usually leaf-opposed; capsules 8-14 in diameter, often purple-blotched; calyx 3.7-6.2 mm long
1 Flowers sessile, with bracteoles immediately subtending the flower; inflorescence of heads or glomerules; flowers sessile or subsessile; capsules or schizocarps 2.5-6 mm across.
....3 Heads or glomerules axillary to well-developed leaves; [section Mougeotia]
....3 Heads or glomerules mainly not associated with leaves, terminal or borne on naked terminal or axillary interrupted spikes; [section Melochia].
......4 Petioles > 1.5 cm long; pubescence of the stem and leaves sparse, of stellate, forked, and/or simple hairs; heads or glomerules of 5-25 flowers, terminal on primary and secondary branches; fruit a capsule
......4 Petioles < 1 cm long; pubescence of the stem and leaves dense (tomentose), of stellate hairs; heads or glomerules of 1-5 (-15) flowers, borne on naked terminal or axillary interrupted spikes with 2-28 heads/glomerules; fruit a schizocarp