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Key to Lactuca

Asteraceae

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)