476- SYNGENESIA NECESSARIA* 
) 
AMBROSIA. Gen. Pe. 
Monoica. Floris 
masculi — involucrum I 
phyllum, haeraispheri- 
cura, multiflorum; an- 
ther ce approximate 
non coalite; receptacu- 
lum nudum. Flor. 
foern. — involucrum 1 
phyllum, sub integer 
aut 5 dentatum; 1 -flo- 
ruit! ; corolla nulla; 
styli 2; mix e calyce 
indurato, 1-sperma. 
Monoecious. Male 
florets — involucrum 1- 
leaved, hemisphaerical, 
many flowered; an- 
thers approximate not 
united; receptacle nak- 
ed. Female florets — 
involucrum 1-leaved, 
entire or 5-toothed, 1 - 
flowered; corolla 0; 
styles 2; nut formed 
from the indurated ca- 
lyx, 1-seeded. 
1. Trifida. Lin. 
Hirsute, rough; 
leaves 3-lobed, serrate, 
the lobes oval-lanceo- 
late, acuminate; fruit 
6-spined below the 
summit. 
Sp. pi. 4. p. 375. Mich. 2. p. 183. Pursh, 2. p. 581. Nutt. 2. p. 186, 
Plant annual, four to eight feet high. Stem hairy, and scabrous. Leaves 
generally opposite, rather large* deeply three-cleft, hairy and scabrous, the 
segments lanceolate, acuminate, serrate. The flowers as in all of this genus 
may be considered as in large terminal panicles composed of axillary and 
terminal spikes. The heads of male florets numerous, solitary, somewhat 
crowded along the summit of the spike; the fertile florets in small clusters of 
two to five at the base, surrounded by two or three bracteal leaves. Invola- 
crum of the male florets one-leaved, five to eight lobed, hairy. Corolla 
small, tubular, white. Stamens distinct. Involucrum of the fertile florets „ 
five-lobed, persistent, germ somewhat obovate, abruptly acuminate. Styles 
two, distinct. Nut one-celled, one-seeded, formed of the indurated involu- 
crum, crowned with six short spines or teeth surrounding the acuminated 
summit. 
] A, hirsuta, aspera; 
foliis 3-lobis, serratis, 
lobis ovali-Ianceolatis, 
acuminatis; fructu in- 
fra apicem 6-spinoso. 
