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1 Flowers pink, purple, or blue, in terminal heads, subtended by an involucre of leaves fused at the base; stem rough-hairy or retrorse-scabrid; [alien]. |
..2 Leaves obtuse at tip; leaves 6-8 per whorl; stem retrorse-scabrid; [clade VI] |
..2 Leaves acute to acuminate at tip; leaves (4-) 6 per whorl; stem rough-hairy; [clade IV] |
1 Flowers white, yellow, or green, in axillary or terminal diffuse inflorescences, not subtended by an involucre; stems either smooth, retrorse-scabrid, or pubescent. |
....3 Largest leaves < 10 mm long; fruits 0.7-1 mm across; annual; [alien]; [clade III]. |
......4 Inflorescence relatively diffuse, branches divaricate; ultimate fruits (2-) 3–6 (-7) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 15-50 mm long; fruit surface glabrous (without hairs) |
......4 Inflorescence relatively strict, branches ascending; ultimate fruits 2-3 (-4) nodes beyond primary stem axis (with largest leaves); first inflorescence internode (beyond primary stem axis) 3-12 (-20) mm long; fruit surface glabrous or bristly-hispid. |
........5 Fruit surface without hairs, smooth to shallowly papillate |
........5 Fruit surface bristly-hispid with uncinate-tipped hairs, distinctly papillate |
....3 Largest leaves > 10 mm long; fruits 1-2.5 mm across; perennial; [native]. |
..........6 Fruits and ovaries uncinate-hispid; leaves 15-50 mm long, 7-10 mm wide; [clade III] |
..........6 Fruits and ovaries glabrous or papillose; leaves 5-25 mm long, 1-6 mm wide. |
............ 7 Corolla 1.5-2.5 mm across, 3-lobed; [collectively widespread in our area]; [clade V]. |
............ ..8 Fruiting pedicels (4-) 5-8 (-12) mm long; pairs of fruits (3-) 3.5-5 mm across at maturity; leaves 2-3 (-4) mm wide |
............ ..8 Fruiting pedicels (2-) 2.5-5 (-6) mm long; pairs of fruits (2-) 2.5-3 mm across at maturity; leaves (1.5-) 2-2.5 (-2.8) mm wide |
............ 7 Corolla 2.5-4.5 mm across, 4-lobed; [mostly of the Mountains in our area, extending into the Piedmont or even the Coastal Plain in n. VA and northward]; [clade undetermined]. |
............ ....9 Leaf margins retrorsely ciliate-scabrid; leaves 3-5× as long as wide; [plants of bogs and moist thickets] |
............ ....9 Leaf margins antrorsely ciliate-scabrid; leaves 4-8× as long as wide; [plants of dry forests and woodlands]. |
............ ......10 Leaves sharply acute or cuspidate; corolla 2.5-3 mm across |
............ ......10 Leaves rounded, obtuse, or barely acute; corolla ca. 4 mm across |