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Key to Lactuca

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1 Achene beaks stout and short, 0.1-0.5 (-1.0) mm long (< ½ as long as the body of the achene); rays blue to violet (rarely yellow or white).
..2 Pappus tawny; flowers mostly 20-30 per head
..2 Pappus bright white; flowers mostly 10-15 per head
1 Achene beaks filiform and long, 1-4 mm long (> ½ as long as the body of the achene); rays yellow or blue (sometimes white or drying bluish).
....3 Each face of the achene with (3-) 5-9 nerves; stems typically white or pale green; rays yellow (sometimes drying blue); leaf midveins typically prickly on the lower surface (except Lactuca sativa) [exotics].
......4 Cypselas purplish to blackish, ellipsoid
......4 Cypselas pale brown, tan, or white, obovoid or oblanceoloid.
........5 Unlobed cauline leaves lanceolate to linear
........5 Unlobed cauline leaves oblong, obovate, or spatulate.
..........6 Phyllaries usually erect in fruit; midribs of leaves usually smooth
..........6 Phyllaries usually reflexed in fruit; midribs of leaves prickly setose
....3 Each face of the achene with 1 (-3) nerves; stems typically medium to dark green or reddish; rays yellow or blue; leaf midveins not prickly on the lower surface, though sometimes with stiff hairs in some species; [natives, though often weedy].
............ 7 Unlobed leaves and lobes of lobed leaves narrow, usually < 1 cm wide; leaves basally disposed, the basal and lower-stem leaves the largest and most persistent; plants 3-12 dm tall; [primarily of the Coastal Plain, rare elsewhere]
............ 7 Unlobed leaves and lobes of lobed leaves wider, usually > 1 cm wide; leaves well-distributed on the stem; plants 3-33 dm tall; [collectively widespread].
............ ..8 Leaves thick textured and with stout prickles along the mid-vein and margins of leaves; [of KY and MS westward]
............ ..8 Leaves without stout prickles along the mid-vein and margins of the leaves (though margins may be toothed); [widespread in our area].
............ ....9 Lobes of leaves mostly widest at the base and tapering to a pointed tip; leaves and stems rarely noticeably pubescent; fruiting involucres 10-15 mm tall; achenes 2.5-3.5 mm long (excluding the beak)
............ ....9 Lobes of leaves blocky, widest above the base and blunt, square or rounded at the tip (like those of a Post Oak); leaves and stem almost always noticeably pubescent; fruiting involucres 15-22 mm tall; achenes 4.5-6 mm long (excluding the beak)
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