EUPHOEBIACEAE 721 



15. Tithymalus obtus^tus (Pursh) Kl. & Garcke. Annual, yellowish green, gla- 

 brous. Stem slender, erect or assurgent, 3-6 dm. high, strict, branched above, topped by 

 a 3— 5-rayed umbel ; rays simple or forked : leaves alternate ; blades spatulate-oblong, 

 obtuse, serrulate to below the middle, sessile, the base slightly auricled : bracts of the rays 

 ovate, cordate, 1-2.5 cm. long: involucres short -peduncled, 1 mm. long, bearing 4 stalked 

 unappendaged glands : capsules subglobose, nearly 4 mm. in diameter, with elongated 

 warts, the lobes rounded : seeds lenticular, oblong, or orbicular-oblong, 1.7-2 mm. long, 

 dark brown, faintly reticulated. \_Euphorbia obtusata Pursh.] 



In dry soil. Pennsylvania to Iowa, South Carolina and Texas. Spring and summer. 



16. Tithymalus Arkansanus (Engelm. & Gray) Kl. & Garcke. Annual or biennial, 

 olive-green, glabrous. Stem rather slender, 2-5 dm. high, topped by a compound 3-rayed 

 umbel, the rays copiously dichotomous : stem-leaves alternate ; blades spatulate or cuneate, 

 1-3 cm. long, acutish, serrate above the middle, sessile : bracts of the rays with triangular 

 or ovate, inequilateral, small, serrate, truncate or cordate blades : involucres solitary in the 

 axils, about 1 mm. long, with 4 elliptic naked nearly sessile glands fully 0.5 mm. long, 

 less than 1 mm. broad : capsules depressed-globose, 2.5-3 mm. broad, with elongated warts : 

 seeds ovoid-lenticular, 1.3-1.5 mm. long, reddish brown, finely but distinctly reticulated. 

 [Euphorbia Arkansana Engelm. & Gray.] 



On plains or prairies, Kansas to Colorado, Alabama and Mexico. Spring and summer. 



17. Tithymalus Missouri6nsis (Norton) Small. Annual or biennial, olive-green. 

 Stem 3-6 dm. tall, topped by a compound 3-rayed umbel : stem-leaves scattered ; blades 

 spatulate, 2-3.5 cm. long, obtuse, serrate to below the middle, the upper ones slightly 

 auricled at the base : bracts of the rays with oblong to ovate, inequilateral, acute, serrate 

 blades : involucres less than 2 mm. high, with 4 oblong glands and glabrous lobes : cap- 

 sules .3-3. 5 mm. in diameter, bearing elongated warts : seeds ovoid, distinctly and regularly 

 reticulated, purplish brown. [^Euphorbia Arkcmsana yar. Missouriensis 1^ or ton.'} 



On plains and prairies, Minnesota to Washington, Kansas and New Mexico. Spring and summer. 



18. Tithymalus leiocdccus ( Engelm. ) Small. Annual, glabrous. Stem branched at 

 the base, the branches ascending or decumbent, 1-2 dm. tall, topped by 2-3-rayed umbels ; 

 rays 2-3.5 cm. long : stem-leaves alternate ; blades spatulate, 0.5-1.5 cm. long, obtuse or 

 retuse at the apex, crenulate-serrate, narrowed into slender bases : bracts of the rays oblong 

 or cuneate-oblong, acute, serrulate above the middle : involucres hemispheric, thin, less 

 than 1 mm. high, longer than the peduncles ; glands transversely oblong, about 0.5 mm. 

 wide : capsules 3-lobecl, 2.5-3 mm. broad, the lobes rounded : seeds flattened, 1.5 mm. long, 

 finely reticulated, dark brown. [_Enphorbia didyosperma var. leiococca Engelm. E. Texana 

 Boiss. ] 



• In dry soil, Texas. Spring. 



29. POINSETTIA Graham. 

 Annual or perennial herbs or shrubby plants, with green or partially, often more highly 

 colored, foliage. Stems simple or branched, often irregularly so. Leaves alternate below, 

 opposite above ; blades similar throughout or very variable : stipules gland-like. Involu- 

 cres in axillary or terminal cymes or solitary : lobes fimbriate. Glands fleshy, solitary, or 

 rarely 3 or 4, sessile or short-stalked, without appendages, the missing ones represented by 

 narrow lobes. Capsule exserted, the lobes rounded. Seed narrowed upward, tuberculate, 

 without a caruncle or with a minute one only. Spurge. 



Gland or glands of the involucre stalked : bracts and upper leaves barely if at all discolored. 

 Leaf-blades linear or linear-lanceolate : seeds not prominently tuberculate : 



glands of the involucre 3 or 4. 1. P. cuphosperma. 



Leaf-blades ovate to ovate-lanceolate : seeds prominently tuberculate : glands of 



the involucre solitary. 2. P. dentata. 



Gland of the involucre sessile or nearly so : bracts and upper leaves discolored at 

 the base. 

 Leaf-blades pilose-bearded at the base, sharply serrate. 3. P. barbellata. 



Leaf-blades not bearded at the base, not sharply serrate. 



Bracts pale at the base. 4. P. geniculata. 



Bracts red, purple or scarlet at the base. 



Upper leaves and bracts with narrowly linear entire blades. 5. P. Havanensis. 



Upper leaves and bracts with broad toothed or lobed blades. 6. P. heterophylla. 



1. Poinsettia cuphosp6rma ( Boiss. ) Small. Annual, usually pubescent. Stems 

 erect, slender, simple or sparingly branched, 2-4 dm. high : leaves opposite or alternate ; 

 blades linear, oblong or linear-lanceolate, 2-8.5 mm. long, entire, undulate, or denticulate, 

 narrowed into a slender petiole : involucres crowded at the ends of the branches, nearly 

 sessile, glabrous or nearly so, almost 4 mm. long, bearing about 4 long-stalked unappend- 

 aged glands : capsules glabrous, or sparingly pubescent, 5 mm. in diameter : seeds narrowly 

 46 



