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Key to Lathyrus

Fabaceae

Lathyrus

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1 Leaflets > 2, generally 4-12; [native species of various habitats].
  2 Foliaceous stipules laterally symmetrical, with 2 approximately equal basal lobes; leaves somewhat fleshy; [plants of ocean beaches and dunes].
    3 lower leaflet surface pubescent (notably on new growth)
  2 Foliaceous stipules asymmetrical, oblique at the base, the basal lobe well-developed only on one side.
      4 Leaflets (8-) 10-14 per leaf, generally irregular arrayed; [plants of dry to mesic forests]
        5 Calyx sparsely to densely pubescent; leaves and stems sparsely to densely pubescent; [mainly Great Lakes and n. Midwest, south to the norther edges of our region]
          6 Lateral lobes of the calyx lanceolate, longer than the calyx tube; [west of the Mississippi River, mainly Interior Highlands, but also upper West Gulf Coastal Plain]
          6 Lateral lobes of the calyx linear-triangular, equal to or shorter than the calyx tube; [mainly Appalachian and Piedmont, NJ and PA south to GA and AL]
      4 Leaflets (4-) 6-10 per leaf, generally paired; [plants of various dry or wet habitats].
             7 Racemes with 5-15 (-20) flowers; corollas white to cream, 10-14 mm long
             7 Racemes with 2-6 (-9) flowers; corollas pink to purple, 15-28 mm long.
               8 Corollas 20-28 mm long; leaflets (4-) 6-10 per leaf; [Great Plainsian, east to c. OK]
               8 Corollas 15-20 mm long; leaflets (4-) 6 per leaf; [northern, south to NC, GA, AL, MO, NE]
1 Leaflets 0-2; [exotic species, except L. pusillus].
                   10 Stems not winged or flanged; corollas 10-15 mm long; flowers 3-10 per inflorescence.
                       12 Stems with wings 0-1 (-2) mm wide; corolla 6-14 mm long; flowers 1-3 (-4) per raceme.
                          13 Legume (in fruit) and ovary (in flower) hirsute with swollen-based hairs; corolla 9-14 mm long
                       12 Stems with wings 1-3 mm wide; corolla 13-30 mm long; flowers 2-12 per raceme.
                            14 Stems hirsute with swollen-based hairs; plant an annual; flowers 2-4 per raceme
                            14 Stems glabrate; plant a perennial; flowers (3-) 4-12 per raceme.