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Key to Eupatorium

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1 Leaves generally in whorls of 3-7 (very rarely all of them opposite), most of them > 2 cm wide; involucre 6.5-9 mm high, the flowers pale pink to purple
1 Leaves generally opposite, sometimes in whorls of 3-4 (if so the leaves usually < 2 cm wide), or some of them alternate; involucre mostly 2-6 mm high, the flowers mostly white, rarely blue (rarely the involucre 6-11 mm high, then the flowers white).
..2 Leaves pinnate or pinnatifid, divided into linear or capillary segments, these 0-5 mm wide (or to 10 mm wide in Eupatorium ×pinnatifidum)
..2 Leaves simple or palmately 3 (-5)-lobed (if palmately lobed, the leaves or lobes > 5 mm wide).
....3 Leaves palmately 3 (-5)-lobed
....3 Leaves simple.
......4 Leaves long-petiolate, the petioles of larger leaves > 10 mm long.
........5 Leaf blades deltate or rhombic, held vertically; [of FL]
........5 Leaf blades lanceolate, held horizontally; [widespread]
......4 Leaves sessile or short-petiolate, the petioles < 9 mm long.
..........6 Florets 7-14 per head.
............ 7 Leaf bases tapering to a cuneate base
............ ..8 Leaves uniformly truncate, usually uniformly coarsely serrate, widest within the lower quarter
............ ..8 Leaves truncate to cuneate (at least at top of stem), usually finely serrate on upper leaves, sometimes coarsely serrate on lower leaves, widest slightly below the middle
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