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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)
............ ..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