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Key to Euphorbia

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1 Shrubs with succulent stems; [subgenus Euphorbia, sect. Crepidaria].

2 Stems zigzag  Euphorbia tithymaloides ssp. smallii

2 Stems straight  Euphorbia tithymaloides ssp. tithymaloides

1 Herbs.

Show caption*© Aidan Campos     3 Leaves strictly opposite, oblique or inequilateral at base; branches prostrate (less usually erect); [subgenus Chamaesyce; section Anisophyllum]  Key to Euphorbia, Key A: subgenus Chamaesyce, section Anisophyllum, subsection Hypericifoliae {add to Key A: E. blodgettii, E. hypericifolia, E. mesembrianthemifolia, E. ophthalmica, E. serpyllifolia var. serpyllifolia}

3 Leaves alternate or opposite, not oblique or asymmetric at base; branches usually erect.

Show caption*© Gary P. Fleming       4 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]  Key to Euphorbia, Key B: subgenus Chamaesyce, section Poinsettia

4 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.

Show caption*© Richard & Teresa Ware         5 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]  Key to Euphorbia, Key C: subgenus Chamaesyce, section Alectoroctonum

5 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

6 Ovary and capsule subtended by a calyx-like structure; seeds without caruncles; involucral gland appendages absent; [subgenus Euphorbia; section Nummulariopsis]  Key to Euphorbia, Key D: subgenus Euphorbia, section Nummulariopsis

6 Ovary and capsule not subtended by a calyx-like structure; seeds with caruncles; involucral gland appendages hornlike or absent; [subgenus Esula]  Key to Euphorbia, Key E: subgenus Esula