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Key to Euphorbia, Key C: subgenus Chamaesyce, section Alectoroctonum

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1 Upper stem leaves and/or dichasial bracts with white margins or entirely white.
..2 Cyathial bracts glabrous, often entirely white (less commonly only white along margins)
..2 Cyathial bracts densely pilose, with conspicuous white margins.
....3 Leaf surfaces pilose; cyathial bracts linear to narrowly oblanceolate; seeds 4.3-4.5 mm long
....3 Leaf surfaces glabrous; cyathial bracts narrowly elliptic to oblanceolate; seeds 3.7-3.9 mm long
1 Upper stem leaves and bracteal leaves entirely green, not whitened.
......4 Leaves opposite, linear-filiform; [primarily of the c. US, w. of the MS river]
......4 Leaves alternate, variously shaped (linear to ovate); [widespread, including c. US].
........5 Petaloid appendages (0.5-) 1.0-4.4 mm long (measured along a radius), about as long as wide or longer, white; stems 1.4-9 (-11) dm tall, erect or ascending.
..........6 Leaves broad (ovate, oblanceolate, elliptic, or lanceolate), < 5.5× as long as wide; leaf blades slightly revolute or planar; glands green.
............ 7 Involucral glands 4; leaf adaxial (upper) surface densely pilose; leaf bases cordate
............ 7 Involucral glands 5; leaf adaxial (upper) surface usually glabrous (besides ciliate margins in E. apocynifolia); leaf bases cuneate to rounded.
............ ..8 Petioles 5-11 mm long; leaves with ciliate margins; cyathia across the appendages ca. 2.5 mm; nodes 7-11 below the umbels; [shady, mesic hardwood forests over limestone or in sand over limestone]
............ ..8 Petioles 0-3.5 (-10) mm long; leaves without ciliate margins; cyathia across the appendages (3.5-) 4–8 (-11) mm; nodes 20-75 nodes below the umbels; [habitats various, generally open, drier, and acidic, e.g., pine woods, sandhills, sandstone, ruderal sites]
............ ....9 Plants (2-) 4-9 (-13) dm tall; aerial stems multiple, (1-) 3-10 stems from a crown, each (1.2-) 2.5-5 (-7) mm in diameter at the base; leaves ascending, leathery, sessile; primary bracts smaller than stem leaves; petaloid appendages oblong or spatulate, 2.5-4.4 mm long; seeds 2.6-3.2 mm long; [NH and MA west to s. ON, MI, WI, MN, and NE, south to se.VA, c. NC, n. GA, s. AL, and e. TX]
............ ....9 Plants 3.5-6.5 dm tall; aerial stems 1 (-3) from a crown, each 1.0-2.2 mm in diameter at the base; leaves usually reflexed, thin, petiolate or subpetiolate; primary bracts similar to stem leaves in size; petaloid appendages orbicular or oval, 0.9-2.2 mm long; seeds 1.8-2.3 mm long; [c. MD, VA, and c. and sw. TN, south to Panhandle FL and s. MS]
..........6 Leaves linear, > 8× as long as wide); leaf blades conspicuously revolute or involute; glands green or dark purple.
............ ......10 Main stem not branching at base, erect or ascending, usually densely pubescent, dark grey or green; leaves not succulent, revolute, petiolate; stipules obsolete; glands green or rarely purple; petaloid appendages entire; [e. and c. GA (or e. SC?) south and west to Panhandle FL and e. TX]
............ ......10 Main stem branching at base, ascending or spreading, glabrous, green or greenish purple; leaves succulent, involute, sessile or short petiole; stipules present and glandular; glands purple; petaloid appendages deeply crenate; [c. and s. peninsular FL]
........5 Petaloid appendages 0.05-0.6 mm long (measured along a radius), shorter than wide, green, red, white, or pink; stems (0.8-) 1.5-4.5 (-6) dm tall, erect, ascending or decumbent; leaves ciliate-margined (E. mercurialina and E. curtisii) or not.
............ ........11 Leaf margins ciliate; cyathia 3.5-5.9 mm wide (across the appendages), green; leaves not fleshy, 1.7-2.2 (-3)× as long as wide, not especially variable; [of mesic forests with rich soils]
............ ........11 Leaf margins not ciliate (except some marginal hairs in E. curtisii); cyathia 2.0-3.4 mm wide (across the appendages), green or maroon; leaves slightly to strongly fleshy, 0.7-20× as long as wide, often very variable in shape, even on the same plant; [of more or less xeric sandhill woodlands with acidic, sandy soils].
............ ..........12 Stems usually 10-18 per crown, decumbent to weakly ascending; leaves opposite (scales on the lower stem sometimes alternate), fleshy, blue-green with a narrow, thickened, red-hyaline margin; branching dichotomous from the base of the plant (the branches typically equal, though sometimes unequal)
............ ..........12 Stems 1-4 (-9) per crown, erect to strongly ascending; leaves alternate, opposite, or in whorls of 3 (at least some alternate on a plant), less fleshy, green to blue-green, without a red margin (or with a very narrow, slightly red-hyaline, but not thickened margin in E. exserta); branching alternate below the inflorescence (rarely dichotomous or trichotomous), the branches typically unequal.
............ ............ 13 Cyathia and capsules green; petaloid appendages white or pink; leaves thin-textured, green, finely pubescent with appressed white hairs (0.1-0.3 mm long) on the lower surface and margins (visible at 10× or greater); branching primarily alternate; leaves primarily alternate (typically opposite or 3-whorled below the inflorescence); cyathia unisexual, plants usually unisexual (dioecious)
............ ............ 13 Cyathia and capsules maroon; petaloid appendages maroon-red; leaves slightly fleshy, somewhat blue-green, glabrous; branching primarily opposite; leaves primarily opposite (usually some alternate on upper branches); cyathia bisexual, plants bisexual
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