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Key to Spermacoce

Rubiaceae

Spermacoce

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1 Calyx with 4 lobes of nearly equal length.
  2 Leaves and stems conspicuously hispid-hirsute; [s. FL]
  2 Leaves and stems glabrous or scabrous; [widespread, including s. FL].
    3 Calyx lobes with a conspicuous central green stripe and white margins, the lobes exceeding the corolla; calyx longer than the corolla
    3 Calyx lobes green throughout (or unicolored), lacking conspicuous white margins (or if with hyaline margins the central green portion wider and extending nearly to the margins).
      4 Flowers in terminal glomerules; stamens exserted; corolla white with a pink throat
      4 Flowers in axillary glomerules; stamens included; corolla white.
        5 Corolla villous in the throat; sepals rotate in fruit, long-deltoid, < 2× as long as width at base; [widespread]
        5 Corolla not villous in throat; sepals erect in fruit, narrowly triangular, > 5× as long as width at base; [s. TX]
1 Calyx with 2 long lobes, the other 2 absent or vestigial (much shorter than the 2 long lobes).
          6 Stems conspicuously winged; trichomes on plant white to red
          6 Stems not winged; trichomes on plant white.
             7 Terminal head (1-) 2-3 cm wide; leaves broadly elliptic, the blade 3-4 cm long, 1.2-1.5 cm wide, obtuse to rounded at the apex
             7 Terminal head 0.5-1 cm wide; leaves linear-lanceolate, acute at the apex.
               8 Plants with many stems branching from the base; terminal inflorescence with 15-30 flowers, heads also at most in the next axil below; corolla tubes 1.5-2.5 mm long, the lobes ca. 2 mm long; fruit (including persistent calyx lobes) 2.5-4.0 mm long; [endemic to pine rocklands in s. FL]
               8 Plants single-stemmed or sometimes many-branched at the base; terminal inflorescence with 30-100+ flowers, heads at 3 or more nodes below; corolla tubes 0.5-1 mm long, the lobes < 1.5 mm long; fruit (including persistent calyx lobes) 2.0-2.5 mm long; [disturbed habitats, nativity uncertain]