370 EUPHORBIACEAE. [Vox.. II. 



over the inner surface of the involucre, consisting of a stamen jointed on a filament-like 

 pedicel, which is subtended by a minute bractlet supposed to represent a calyx. Pistillate 

 flower solitary, consisting of a 3-celled ovary at the bottom of the involucre, at length usually 

 exserted on a stalk; styles 3, 2-cleft. Capsule erect or nodding, 3-lobed, separating into 3 2- 

 valved carpels. Seeds sometimes caruncled, often ash-colored, variously pitted, ridged or 

 wrinkled. [Named in honor of Euphorbus, King Juba's physician.] 



Species about 700, most abundant in the warmer parts of the temperate zones. Besides the 

 following, some 95 others occur in the southern and western parts of North America. 



& Glands of the involucre with petal-like appendages, 

 t Leaves opposite, somewhat inequilateral, their bases more or less oblique. 



J Leaves entire; seeds smooth. 



Plants branched at the base, the branches prostrate. 



Seeds i J4" long. i. E. polygonifolia. 



Seeds J<"-K" long. 



Leaves usually more than twice as long as broad; seeds nearly terete, %" long. 



4. E. Geyeri. . 

 Leaves usually less than twice as long as broad; seeds obtusely 4-angled, %" long. 



5. E. serpens. 

 Plants with an erect or ascending stem, branched above, the branches ascending. 



Seeds nearly terete, i" long; leaves usually flat and straight. 2. E. petaloidea. 

 Seeds 4-angled, -K" long; leaves often involute and curved. 3. E. Nultallii. 



J t Leaves entire; seeds variously roughened. 



Plants glabrous. 1 1 . E. Fendleri. 



Plants canescent. 12. E. /a/a. 

 J J J Leaves serrate or dentate; plants prostrate or spreading. 

 Herbage glabrous. 



Seeds faintly transversely ridged and pitted. 6. E. serpyllifolia. 



Seeds strongly transversely ridged, not pitted. 7. E. glyptospcrma. 

 Herbage pubescent, or puberulent. 



Seeds gray or ash-colored, pitted. 10. E. strictospora. 

 Seeds brown or black. 



Involucres not split. 8. E. macitlala. 



Involucres split on one side. 9. E. humislrata. 



tit i Leaves serrate or dentate; plants erect or ascending. 13. E, nutans. 



t t Leaves opposite, equilateral, their bases not oblique. 14. E. hevagona, 

 t t t Leaves alternate or scattered on the stem, except a whorl subtending the umbel. 



Bracts and leaves of the umbel small and green; seeds ovoid, smooth, sparingly pitted. 



15. E. corolla/a. 

 Bracts and leaves of the umbel large, white-margined; seeds ovoid-globose, reticulate-tuberculate. 



16. E. marginala. 

 X- -Jt Glands of the involucre naked (without petal-like appendages). 



t Leaves mostly opposite; herbage glabrous. 



Plants slender; stems or branches forked. 



Annual; stem branched at the base; leaves, or some of them, oblique at the base. 



i. E. polygonifolia. 



Perennial; stems several from a stout root; leaves not oblique at the base. 19. E. Ibecacuanhae, 

 Plants stout; stem usually simple below, topped by an umbel. 21. E. Lathy ris. 



t t Leaves mostly opposite ; herbage pubescent. 



Leaves linear or linear-lanceolate; seeds narrowly-ovoid, not prominently tuberculate. 



17. E. cupliosperma. 

 Leaves ovate or ovate-lanceolate; seeds broadly ovoid, prominently tuberculate. 



18. E. dentata. 

 t t t Leaves alternate or scattered. 



Stem not topped by an umbel. 20. E. heterophylla. 



Stems topped by a several-rayed umbel. 



Leaves serrulate; glands of the involucre oblong, oval or orbicular. 

 Seeds smooth or faintly reticulated. 



Glands stalked; warts on the capsules elongated; seeds faintly reticulated. 



23. E. obtusata. 



Glands sessile; warts on the capsules depressed; seeds smooth. 24. E. platyphylla. 

 Seeds strongly and prominently reticulated. 



Glands nearly sessile; capsules warty. 25. E. dictypsperma. 



Glands stalked; capsules smooth. 26. E. Helioscopia. 



Leaves entire; glands of the involucres crescent-shaped or reniform. 

 Plants perennial; seeds smooth. 

 Glands crescent-shaped, horned. 



Stem-leaves 2" -6" broad; capsules smooth. 



Leaves subtending the umbel lanceolate or oblanceolate. 29. E. Esula. 

 Leaves subtending the umbel ovate, oval or obovate. 30. E. Nicaeensis. 

 Stem-leaves X"-iM" broad; capsules granular on the lobes. 31. E. Cyparissias. 

 Glands reniform, not horned. 22. E. Darlingtonii. 



Plants annual or biennial; seeds pitted or rugose-pitted. 

 Leaves thin, petioled. 



Capsules with 2-crested lobes. 27. E. Peplus. 



Capsules with rounded lobes. 28. E. commutata. 



Leaves thick, sessile. 32. E. robusta. 



