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| Euphorbia tirucalli |
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3. | Spines arising from separate tubercles; cyathophylls prominent, red or yellow |
| Euphorbia milii |
3. | Spines paired on each spine-shield; cyathophylls not prominent, usually scarious |
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4. | A densely-branched shrub, not forming a trunk |
| Euphorbia caducifolia |
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| Euphorbia nivulia |
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6. | Angles not produced into wings |
| Euphorbia neriifolia |
6. | Angles produced into undulate wings |
| Euphorbia royleana |
1. | Plants woody or herbaceous |
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7. | Stipules present, sometimes much-reduced |
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8. | Leaves all opposite, asymmetrical at the base; stipules scarious, persistent; glands usually appendiculate |
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9. | Cyathia aggregated together into clusters |
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10. | Leaves rhombic; hairs multicellular, yellow; cyathia in dense, axillary, pedunculate clusters |
| Euphorbia hirta |
10. | Leaves oblong; hairs mostly unicellular, white; cyathia in loose clusters terminating lateral shoots |
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11. | Plants puberulous or pubescent |
| Euphorbia indica |
| Euphorbia hypericifolia |
9. | Cyathia axillary, solitary, often borne on pecialized lateral shoots |
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12. | Plant completely glabrous, rooting at the nodes; stipules fused to form a triangular scale above and beneath |
| Euphorbia serpens |
12. | Plant glabrous, puberulous, pubescent or hispid, not rooting at the nodes; stipules all free, or only the pairs beneath fused into a scale |
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13. | Leaves entire or almost so |
| Euphorbia granulata |
13. | Leaves minutely denticulate, serrulate, or serrate |
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14. | Glands with prominent white appendages |
| Euphorbia hispida |
14. | Gland-appendages minute or absent |
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15. | Plant completely glabrous; leaf-blades narrowly falcate-oblong |
| Euphorbia clarkeana |
15. | Plant puberulous or pubescent above, glabrous beneath; leaf-blades obovate-suborbicular or ovate-oblong |
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16. | Fruits glabrous except on the keels; seeds sharply transversely-ridged |
| Euphorbia prostrata |
16. | Fruits adpressed-pubescent; seeds shallowly transversely-ridged |
| Euphorbia thymifolia |
8. | Leaves mostly opposite or else alternate, whorled and opposite, symmetrical at the base; stipules subulate, persistent or fugacious, or sessile and glandular; glands usually exappendiculate |
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17. | Uppermost leaves of the pseudumbel with conspicuous white margins; stipules fugacious |
| Euphorbia marginata |
17. | Uppermost leaves of the pseudumbel red, green or yellow; stipules persistent |
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18. | Cyathia usually with 4-5 pectinate glands; stipules subulate, eglandular |
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19. | Leaves linear to ovate; stipules 1 mm long |
| Euphorbia cheirolepis |
19. | Leaves all ovate or elliptic-ovate; stipules 0.25 mm long |
| Euphorbia petiolata |
18. | Cyathia with only 1 cupular, circular or saccate gland, or rarely glands 2-3; stipules sessile, glandular |
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20. | Leaves elliptic-obovate, elliptic-lanceolate or lanceolate |
| Euphorbia heterophylla |
20. | At least the lower leaves panduriform |
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21. | Upper leaves green with a basal red blotch |
| Euphorbia cyathophora |
21. | Upper leaves uniformly bright scarlet |
| Euphorbia pulcherrima |
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22. | Leaves opposite or whorled, rarely any alternate; annuals |
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23. | Caruncle stipitate, the stalk 0.3-0.5 mm long |
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24. | Leaves linear, less than 2 mm wide; glands ecornute |
| Euphorbia inderiensis |
24. | Leaves linear-lanceolate, more than 2 mm wide; glands cornute |
| Euphorbia sororia |
23. | Caruncle sessile or subsessile |
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25. | Leaves ovate to linear-lanceolate; glands ecornute |
| Euphorbia aserbajdzhanica |
25. | Leaves spathulate to suborbicular; glands cornute |
| Euphorbia densa |
22. | Leaves alternate, whorled and opposite, or, if any stem-leaves opposite, then decussate; annuals, biennials or perennials |
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26. | Pseudumbels usually borne on short lateral beanches |
| Euphorbia osyridea |
26. | Pseudumbels usually terminal |
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27. | Leaves commonly coarsely and irregularly sharply denticulate |
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| Euphorbia grossheimii |
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29. | Stem-leaves not more than 3 cm long; glands madder, maroon or black |
| Euphorbia tibetica |
29. | Stem-leaves up to 7 cm long; glands ochreous |
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30. | Stem-leaves linear to oblong-lanceolate; fruits 6 x 5 mm |
| Euphorbia caeladenia |
30. | Stem-leaves oblong-lanceolate to orbicular-ovate; fruits 4.5 x 4.5 mm |
| Euphorbia multifurcata |
27. | Leaves entire, subentire or minutely and regularly serrulate or denticulate |
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31. | Glands rounded on the outer edge |
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33. | Plant 10-20 cm tall; pseudumbel 3-5-rayed |
| Euphorbia micractina |
33. | Plant 40-100 cm tall; pseudumbel 5-15-rayed |
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34. | Leaves subentire or serrulate; fruits densely covered with conical warts |
| Euphorbia cornigera |
34. | Leaves entire; fruits sparingly warty |
| Euphorbia cognata |
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| Euphorbia helioscopia |
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| Euphorbia jacquemontii |
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37. | Stem-leaves elliptic-ovate or elliptic, 1-5 cm long |
| Euphorbia thomsoniana |
37. | Stem-leaves ovate-lanceolate or elliptic-lanceolate, 4-11 cm long |
| Euphorbia wallichii |
31. | Glands truncate, crescentic or 2-(rarely more-) horned |
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39. | All leaves linear to linear-lanceolate |
| Euphorbia dracunculoides |
39. | Leaves variable, the upper differing from the stem-leaves |
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40. | Stem-leaves petiolate; fruits 2-ridged on the keels |
| Euphorbia peplus |
40. | Stem-leaves sessile; fruits with rounded keels |
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41. | Ray-leaves cuspidate-aristate |
| Euphorbia falcata |
41. | Ray-leaves obtuse or rounded |
| Euphorbia maddenii |
38. | Biennial or perennial herbs |
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42. | Stem-leaves opposite, decussate; fruit spongy |
| Euphorbia lathyris |
42. | Stem-leaves alternate; fruit hardened |
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43. | Glands truncate, hornless |
| Euphorbia seguieriana |
43. | Glands truncate or crescentic, usually 2-horned |
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44. | Plants decumbent- or procumbent ascending |
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45. | Seeds ovoid-hexagonal; NWFP & Kashmir |
| Euphorbia kanaorica |
45. | Seeds compressed-ovoid; Baluchistan |
| Euphorbia aucheri |
44. | Plants erect, rarely ascending |
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46. | All leaves linear-lanceolate; seeds tuberculate-rugulose |
| Euphorbia dracunculoides |
46. | Upper leaves differing from the stem-leaves |
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47. | Pseudumbel-rays often proliferating as densely-leafy shoots |
| Euphorbia prolifera |
47. | Pseudumbel-rays not proliferating |
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48. | Stem-leaves usually obovate or oblanceolate |
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49. | Pseudumbel-rays rarely more than once or twice bifid; Baluchistan |
| Euphorbia microsciadia |
49. | Pseudumbel-rays commonly 4-5 times bifid; NWFP, N. Punjab & Kashmir |
| Euphorbia maddenii |
48. | Stem-leaves usually linear or lanceolate |
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50. | Plant not exceeding 25 cm in height; ray leaves usually trullate |
| Euphorbia talaina |
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51. | Stem-leaves lanceolate; ray-leaves ovate-deltoid; glands truncate, 2-horned |
| Euphorbia thyrsoidea |
51. | Stem-leaves usually linear; ray-leaves transversely elliptic to suborbicular; glands crescentic |
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52. | Stem-leaves more than 1 cm wide |
| Euphorbia boissieriana |
52. | Stem-leaves not more than 8 mm wide |
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53. | Stem-leaves up to 8 mm wide |
| Euphorbia cyrtophylla |
53. | Stem-leaves not more than 4 mm wide |
| Euphorbia pamirica |