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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}

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1 Young stems and leaves glabrous; leaves either entire or serrulate, at least at the apex (use 10× magnification).

2 Leaves serrulate, at least at the apex (use 10× magnification); seeds with 2-4 transverse ridges.

3 Seeds 1.0-1.3 mm long, with 3-4 (-6) transverse ridges; involucre 0.6-0.9 mm long; stems prostrate; [s. IN and c. TN westward, primarily w. of MS river]  Euphorbia glyptosperma

3 Seeds 0.8-1.1 mm long, with 2-4 transverse ridges; involucre 0.9-1.1 mm long; stems erect to ascendant; [SC s. to FL and w. to TX in our region].

4 Stipules conspicuous, 1.0-1.5 mm long; stems glabrous throughout; plants to 50 cm long; capsules 1.1-1.5 mm wide; seeds 0.9-1.1 mm long, with low, smooth ridges and shallow depressions between  Euphorbia hypericifolia

4 Stipules inconspicuous, ca. 0.5 mm long; stems (at least sparsely) pilose proximally and glabrous distally; plants to 80 cm long; capsules 1.7-1.8 mm wide; seeds 1.0-1.4 mm long, with 2-3 prominent transverse ridges  Euphorbia hyssopifolia

2 Leaves absolutely entire; seeds smooth.

5 Stipules united into a triangular scale-like structure (this often lobed or fringed), thus appearing as 2 stipules at each node  Euphorbia serpens

5 Stipules separate, lacerate, appearing as 3 or 4 stipules at each node.

6 Mature seeds bluntly angled or subangled in cross section, 1.0-1.4 (1.6) mm long (except for 1.8-2.1 mm long in E. cordifolia); leaves either 1.5-2× or 4-5× as long as wide, not fleshy; [sandy inland habitats or coastal dunes in E. cumulicola].

7 Leaves 1.5-2× as long as wide, green throughout; [more widespread].

7 Leaves 4-5× as long as wide, the leaf margin red; [FL]  Euphorbia cumulicola

8 Seeds ashy white with a brown longitudinal line on adaxial surface, 1.1-1.4 (-1.6) mm long; leaf bases angled or rounded, with one side of the leaf base often expanded into a small rounded auricle  Euphorbia geyeri var. geyeri

8 Seeds gray or tan with dark brown mottling, 1.8-2.1 mm long; leaf bases cordate to rounded, without an auricle on one side  Euphorbia cordifolia

6 Mature seeds rounded in cross section, (1.3-) 1.5-2.6 mm long; leaves 2-3 (-5)× as long as wide, often somewhat fleshy; [of barrier island dunes and other sandy coastal habitats].

9 Mature seeds (1.3-) 1.5-1.9 mm long; cyathia terminal on the stems and also axillary  Euphorbia bombensis

9 Mature seeds (2.0-) 2.2-2.6 mm long; cyathia terminal on the stems  Euphorbia polygonifolia

1 Young stems and leaves pubescent (at least in lines along the stems); leaves serrulate, at least at the apex (use 10× magnification).

10 Ovary and capsule glabrous.

11 Seeds 0.8-1.0 mm long, light gray, the faces with 2-3 (-4) horizontal, low, blunt ridges, sometimes connected by 1-2 cross ridges; stems glabrous when young (uncommonly puberulent along 1 side of the branchlets); capsule 1.5-2.0 mm long  Euphorbia hyssopifolia

11 Seeds 1.0-1.3 mm long, dark gray, faces without ridges, though irregularly and finely wrinkled; stems puberulent when young on 1 side only; capsule 2.0-2.5 mm long.

12 Stems ascending or suberect, puberulent when young  Euphorbia nutans

12 Stems prostrate or widely spreading, spreading-hirsute  Euphorbia vermiculata

10 Ovary and capsule pubescent.

Show caption*© Scott Ward                           13 Stems with 2 types of trichomes, the longer 3-5 mm long; cyathia in axillary and terminal cymes, at least some of the peduncles > 10 mm long  Euphorbia hirta

13 Stems with 1 type of trichome, these < 2 mm long; cyathia solitary or several in axils, the peduncles < 5 mm long.

14 Capsules spreading-villous, especially or solely on the angles; styles 0.2-0.3 mm long, bifid nearly to the base; seeds sharply quadrangular-angled, the faces with 3-4 transverse ridges  Euphorbia prostrata

14 Capsules minutely appressed-puberulent, on the entire surface (though sometimes primarily on the lower portion); styles 0.3-0.7 mm long, bifid only in the upper half or third; seeds quadrangular but not angled, the faces with inconspicuous transverse ridges or nearly smooth.

15 Involucre cleft on 1 side half its length; leaves mostly obovate, 1.5-2× as long as wide; styles 0.5-0.7 mm long, filiform; seed faces nearly smooth; adventitious roots formed at middle nodes along the stem  Euphorbia humistrata

15 Involucre cleft on 1 side a fourth to a third its length; leaves mostly oblong, 2-3× as long as wide; styles 0.3-0.4 mm long, clavate; seed faces transversely ridged; adventitious roots not formed  Euphorbia maculata