164: 
COMPOSITAE 
decumbent or prostrate base, 1.4 to 2.4 dm. high; leaves narrowly obovate 
to linear, entire, sessile; heads solitary in the axils, short-peduncled; 
bracts of the involucre united into a lobed or toothed cup.—Alkaline 
plains and borders of salt marshes. 
18. AMBROSIA L. Ragweed 
Coarse aromatic perennial herbs with alternate pinnatifid leaves. 
Flowers inconspicuous, unisexual. Staminate heads in catkin-like ra¬ 
cemes ; involucres broadly hemispherical, many-flowered; corollas funnel- 
form, 5-lobed. Pistillate heads in axils of upper leaves at the base of the 
staminate racemes; involucres turbinate, 1-flowered; corollas none. 
Pappus none. Fruit an achene-like bur armed with a single row of 
prickles. (Ancient Greek name.) 
1. A. psilostachys DC. Western Ragweed. Stems simple, erect, 3 
to 8.6 dm. high, from slender running rootstocks; herbage pubescent; 
leaves once or twice pinnatifid; fruit a bur bearing 4 protuberances, or 
unarmed.—Uncultivated lands. 
19. XANTHIUM L. 
Coarse branching weeds. Leaves alternate, toothed or lobed. Heads 
unisexual. Staminate heads subglobose, in a terminal cluster, many- 
flowered ; involucre a single row of distinct narrow bracts; corollas tubu¬ 
lar. Pistillate heads axillary ; involucre closed, 2-flowered; corolla none. 
Pappus none. Fruit a bur covered with hooked prickles. (Greek xan- 
thion, yellow, from its yielding a hair-dye of that color.) 
1. X. spinosum L. Spiny Clotbur. Stems much branched, with yel¬ 
lowish 3-pronged spines beside the leaves; leaves lanceolate, 2 or 3-lobed 
or cut, green above, white pubescent beneath; corolla rusty-pubescent; 
bur sparsely prickly.—Barnyards and neglected fields; nat. from Eur. 
2. X. canadense Mill. Cockle Bur. Stems about 3 to 6 dm. high, 
not prickly; leaves deltoid-ovate, irregularly serrate or incised, often 
3-lobed, rough, green on both sides; bur glandular-pubescent on the body, 
spiny, bearing at apex a pair of strong beaks hooked or incurved at tips.— 
Low or marshy lands; nat. from the eastern U. S. 
20. BAERIA F. & M. Gold Fields 
Low mostly slender commonly hairy annuals. Leaves opposite, linear. 
Flowers yellow. Rays 5 to 15, showy or short. Involucre hemispherical, 
its bracts as many as the rays. Receptacle subulate-conical. Pappus of 
paleae or awns or both or none. (The Russian zoologist, Baer.) 
1. B. chrysostoma F. & M. Gold Fields. Stems slender, simple or 
branching, 1.2 to 2.6 dm. high; leaves narrowly linear, entire; achenes 
smooth, shining or papillate; pappus typically none.—Lower foothills 
and valley plains. Var. gracilis Hall. Achenes more or less strigose- 
pubescent; pappus of 3 or 4 awns from small lanceolate paleae, some¬ 
times none.—Mid. Cal. to S. Cal. 
21. LASTHENIA Cass. 
Glabrous annuals with opposite entire sessile leaves. Flowers yellow, 
with 5 to 15 rays. Bracts of involucres more or less united into a 
toothed cup. Receptacle conical, covered with points which bear the 
