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Key to Euphorbia

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1 Plants shrubs or subshrubs with succulent stems OR abundant stem spines; [subgenus Tirucalli OR subgenus Euphorbia (sections Crepidaria and Goniostema); FL].
  2 Plants bearing succulent stems only, without broadened leaves; [subgenus Tirucalli]
  2 Plants with broad leaves, not merely just long thin green succulent stems.
    3 Stems with abundant spines; [sect. Goniostema]
    3 Stems succulent, lacking abundant spines; [sect. Crepidaria].
      4 Stems zigzagged
      4 Stems straight
1 Plants herbaceous, lacking succulent or spiny stems; [subgenus Chamaesyce; Esula; Poinsettia; Euphorbia (sect. Nummulariopsis); widespread, including FL]
image of plant
Show caption*© Aidan Campos
        5 Leaves strictly opposite, oblique or inequilateral at base; branches prostrate (less usually erect); [subgenus Chamaesyce; section Anisophyllum]
        5 Leaves alternate or opposite, not oblique or asymmetric at base; branches usually erect.
image of plant
Show caption*© Gary P. Fleming
          6 Bracteal leaves lobed or toothed (rarely linear), usually marked with red or white at the base or purple-spotted; glands of the cyathia usually 1 (rarely more), bilabiate, lacking petaloid appendages; [subgenus Chamaesyce; section Poinsettia]
          6 Bracteal leaves entire, not marked with red (white-margined in E. marginata); glands of the cyathia 4-5, flattish, not bilabiate, with or without petaloid appendages.
image of plant
Show caption*© Richard & Teresa Ware
             7 Glands of the cyathia 5 (or 7-10 on the central cyathium in E. pubentissima), with petaloid appendages 0.1-5.0 mm long (measured along a radius), these white, maroon, red, pink, or green; stipules present, glandlike, often minute; [subgenus Chamaesyce; section Alectoroctonum]
             7 Glands of the cyathia 4 (except 5 in E. purpurea), oval, reniform, or crescent-shaped, lacking petaloid appendages (the glands themselves yellowish or green); stipules absent or vestigial
               8 Ovary and capsule subtended by a calyx-like structure; seeds without caruncles; involucral gland appendages absent; [subgenus Euphorbia; section Nummulariopsis]
               8 Ovary and capsule not subtended by a calyx-like structure; seeds with caruncles; involucral gland appendages hornlike or absent; [subgenus Esula]