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Key to Eutrochium

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1 Florets (4-) 6-9 (-12) per head; leaves more or less 3-nerved from the base, rather abruptly contracted to the short petiole, thick in texture, 5-12 (-15) cm long, strongly resin-dotted beneath; leaves in whorls of (2-) avg. 3-4 (-5); stem generally purple-speckled (sometimes uniformly purple); [primarily of the Coastal Plain]
1 Florets either (8-) 9-22 or 4-7 per head; leaves generally pinnately veined (rarely with a tendency to be 3-nerved), usually cuneate and less abruptly contracted to the petiole, thick or thin in texture, 6-35 cm long, weakly or not at all resin-dotted beneath (except often strongly resin-dotted in E. maculatum); leaves in whorls of (2-) 3-7; stem purple-speckled, purple at the nodes, purple throughout, or green; [collectively widespread in our area].
..2 Florets (8-) 9-22 per head; leaves mostly in whorls of (3-) avg. 4-5 (-6), 6-20 cm long; inflorescence more or less flat-topped; stem usually speckled with purple (rarely evenly purplish).
....3 Middle and lower portions of stems densely puberulent; leaves densely puberulent below, relatively thick in texture; [MO and northwards and westwards]
....3 Middle and lower portions of stems glabrous (sometimes puberulent upwards); leaves usually glabrate, relatively thin in texture; [IL, KY, TN, and GA northwards and eastwards]
..2 Florets 4-7 per head; leaves in whorls of (2-) 3-7, 8-35 cm long; inflorescence rounded; stem usually purple throughout, purple at the nodes, or lacking purplish pigment.
......4 Stem hollow (with a large central cavity), purple throughout, strongly glaucous when fresh; flowers bright pink-purple; leaves in whorls of (3-) avg. 5 (-7); leaves mostly 3.5-5.5× as long as broad
......4 Stem solid (rarely with a slender central cavity), dark purple at the nodes or greenish purple throughout, not glaucous or only slightly so when fresh; flowers pale pink-purple; leaves in whorls of (2-) avg. 3-4 (-5); leaves mostly 2-4× as long as broad.
........5 Stem persistently glandular-pubescent throughout; lower surface of leaves glandular-pubescent; leaves mostly 2-2.5× as long as wide; stem greenish-purple (or evenly purple); [of the Mountains]
........5 Stem glandular-puberulent in the inflorescence, glabrous below the inflorescence; lower surface of leaves with few, sessile resin dots; leaves mostly 2.5-4× as long as broad; stem greenish, often dark purple at the nodes, particularly when sun-grown; [collectively widespread in our area].
..........6 Leaves ovate to broadly elliptical, the apex acute to obtuse; leaf teeth acute to blunt, 1-serrate; leaf lower surface densely softly lanulose on the surface and the veins; achenes with many long-papillate glands at anthesis; [apparently narrowly distributed in the Piedmont of NC, SC, and GA]
..........6 Leaves broadly lanceolate to ovate, the apex acuminate to acute; leaf teeth sharply 1-2-serrate; leaf lower surface usually glabrate (slightly to densely softly lanulose on the veins only, or densely lanulose across the surface in var. holzingeri, distributed in the western part of our region); achenes with sparse to medium short-papillate glands at anthesis; [widespread in our area].
............ 7 Leaf lower surface densely lanulose on the veins and the surface; [MO and n. AR, northwards and westwards]
............ 7 Leaf lower surface glabrous, or sparsely hairy along the main veins; [widespread in our region]
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