EUPHORBIACEAE 721 
15. Tithymalus obtusàtus (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 : bract$ of the rays 
ovate, cordate, 1-2.5 cm. long: involueres short-peduncled, 1 mm. long, bearing 4 stalked 
unappendaged glands: capsules subglobose, nearly 4 mm. in diameter, with elongated 
warts, the "abis 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 Arkansànus (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 em. 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. & Gry: T 
On plains or prairies, Kansas to Colorado, Alabama and Mexico. Spring and summer. 
17. Tithymalus Missouriénsis (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 Arkansana var. Missouriensis Norton. } 
On plains and prairies, Minnesota to Washington, Kansas and New Mexico, Spring and summer, 
18. Tithymalusleiocóccus (Engelm.) Small. Annual, glabrous. Stem branched at 
the base, the branches ascending or decumbent, 1-2 dm. tall, € 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-lobed, 2.5-3 mm. broad, the lobes rounded : seeds flattened, 1.5 mm. long, 
re remet dark brown. [Euphorbia dictyosperma var. leiococca Engelm. E. Terana 
iss. 
In dry soil, Texas. Spring. 
29. POINSÉTTIA 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 ee 2, P. dentata. 
Tia: ^ the involucre sessile or nearly so: bracts and upper leaves discolored at 
Leaf-blades pilose-bearded at the base, sharply serrate. 8. P. barbellata. 
Leaf-blades not bearded at the base, not duri serrate. 
Braets pale at the base. 4. P. geniculata. 
Braets 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 cuphospérma (Boiss.) Small Annual, usually pubescent. Stems 
erect, slender, simple or sparingly branched, 2-4 dm. high : leaves copon 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, nearl 
sessile, glabrous or nearly so, almost 4 mm. long, bearing about 4 long-stalked nedum d 
glands : capsules glabrous, or sparingly pubescent, 5 mm. in diameter : seeds narrowly 
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