536 MISC. PUBLICATION 42 3, U. S. DEPT. OF AGRICULTURE 



6. Involucral glands either dentate or with horns and lunate; capsule smooth 

 or hairy but never verrucose or papillate; seeds not obviously reti- 

 culate but often mottled or rugulose, usually grayish; leaves nearly 

 always entire; plants perennial (8). 

 8. Stems robust, strictly erect, mostly 2 to 5 mm. thick at the base, mostly 

 30 to 55 cm. high, with densely leafy sterile branches on the upper 

 half below the whorled leaves; stem leaves narrowly oblong to 

 oblong-lanceolate, glabrous, glaucous, subsessile; capsule 4 to 5 mm. 



long; seeds truncate at base 7. E. chamaesula. 



8. Stems mostly either shorter or more slender, without sterile leafy 

 branches; stem leaves various, often pubescent or papillate; capsule 

 often shorter; seeds rounded at base (9). 

 9. Stem leaves either elliptic and tapering equally to the acute apex and 

 the petioled base, or (at least the upper ones) widest well below 

 the middle; leaf epidermis not papillate (10). 

 10. Stem leaves, at least the upper ones, widest near the base, sub- 

 cordate, subsessile 13. E. robusta. 



10. Stem leaves elliptic and tapering equally to the acute apex and 

 the petioled base; stems mostly slender (about 1.5 mm. thick), 

 mostly numerous and often sinuous (11). 

 11. Glands irregularly toothed all along the margin, without 



horns exceeding the teeth 10. E. incisa. 



11. Glands with sharp horns about one-half as long as the gland, 

 otherwise essentially entire (12). 

 12. Stems more than 20 cm. long; rays commonly repeatedly 

 branched, often forming a dense inflorescence in age. 



8. E. BRACHYCERA. 



12. Stems only about 20 cm. long; rays commonly once or twice 



forked 9. E. odontadenia. 



9. Stem leaves either orbicular to elliptic-oblong and obtuse, or obviously 

 widest above the middle; leaf epidermis often papillate (13). 

 13. Kays of the pleiochasium mostly 3; first pair of floral leaves often 

 deltoid, usually longer than wide; leaf epidermis not papillate. 



8. E. BRACHYCERA. 



13. R&ys of the pleiochasium mostly 5; floral leaves all broadly 

 rounded; leaf epidermis usually papillate (14). 

 14. Stem leaves mostly oblong to suborbicular; floral leaves wider 



than long 11. E. palmeri. 



14. Stem-leaves spatulate to oblanceolate; floral leaves about as 



wide as long 12. E. lurida. 



1. Glands of the involucre with petaloid appendages or, if the appendages wanting, 

 the leaves all strictly opposite and with inequilateral bases (15). 

 15. Leaves alternate, opposite, or even whorled, symmetric at base; stipules 

 glandlike or none: Subgenus Agaloma (16). 

 16. Stems branched above into a 3- (rarely 4-) rayed, essentially symmetric 

 pleiochasium; floral leaves with broad white margins. 



14. E. MARGINATA. 



16. Stems often forking above, never branching into a cyme with more than 

 2 branches; floral leaves green throughout (17). 

 17. Plant perennial with a thickened root; seeds smooth, ovoid. 



15. E. plummerae. 

 17. Plant annual with slender roots; seeds definitely angled (18). 



18. Leaves all entire; appendages all symmetrically bifid to the base; 



seeds often dull black 16. E. bilobata. 



18. Leaves, at least some of them, serrulate to serrate; appendages entire 

 to irregularly toothed; seeds brown to sordid white. 



17. E. exstipulata. 

 15. Leaves all strictly opposite, usually strongly inequilateral at base; stipules 

 mostly well developed, always evident in species with symmetric leaves: 

 Subgenus Chamaesyce (19). 

 19. Ovary and capsule pubescent (20). 



20. Plant perennial but flowering the first year; staminate flowers 16 to 60 

 (rarely as few as 15 in E. melanadenia) ; appendages never markedly 

 unequal; involucres never urceolate (21). 

 21. Cyathia borne in dense glomerules, a few sometimes also solitary in 



the upper forks; leaves often serrate 23. E. capitellata. 



21. Cyathia solitary in the axils and at the tips of the branches; leaves 

 always entire (22). 



