SYNGENESIA NECESSARIA. 
479 
1. Strumarium. 
X. caule inermi, ra- 
moso; foliis cordatis, 
lobatis, serratis, sca- 
bris, trinervibus; fruc- 
tibus ellipticis, pubes- 
ceatibus, setis rigidis 
uncinatis. 
Stem unarmed, 
branching; leaves cor- 
date, lobed, serrate, 
scabrous, three-nerved; 
fruit elliptic, pubescent, 
armed with rigid hook- 
ed bristles. 
Sp. pi. 4. p. 373. Mich. 2. p. 182. Pursh, 2. p. 581. Nutt. 2. p. 186. 
X. Americanum, Walt. p. 231. 
Plant annual. Stem three to six feet high, branching, angled, pubescent, 
and very scabrous. Leaves alternate, generally three-lobed, the lobes 
coarsely toothed, pubescent and very scabrous on both surfaces, six to eight 
inches long, nearly of the same width, on petioles three to four inches long. 
Heads of male jiorets arranged on axillary racemes. Leaves of the involu- 
crura subulate. Stamens united at base. Anthers distinct. Chaff of the 
receptacle subulate. F ertile jiorets one or two at the base of each raceme. 
Involucrum ten-leaved, two-flowered, the leaflets subulate, equal. Proper 
calyx an arillus? oblong, armed with hooked prickles of which the two at the 
summit become much larger than the others. Seed oblong, inclosed in the 
persistent calyx. 
The germs in this plant which when young appear to be distinct, unite as 
they mature and form a two-celled bipartible? fruit. 
Grows in fields and about buildings — very common but not indigenous. 
Flowers July — October. Sheep-bur. 
2. Spinosum. 
X. spinis ternatis; Spines ternate; leaves 
foliis trilobis. three-lobed. 
Sp, pi. 4. p. 374. Nutt. 2. p. 186. 
Annual. Stem three to five feet high, terete, pubescent. Leaves alter- 
nate, ovate-lanceolate, acute, when young entire, when old, three-lobed, 
pale green, pubescent on the upper surface, almost tomentose underneath. 
Petioles two to three lines long, a spine three-forked, rigid, about an inch 
long, grows on one side of each petiole. Heads of male jiorets solitary, 
axillary at the base of each spine. Involucrum many leaved; leaves ovate. 
Filaments longer than the corolla, united at base. Anthers distinct. F er- 
tile jiorets solitary, axillary, opposite the spine. Proper calyx armed with 
short hooked prickles. Styles two. Fruit two-celled. 
An exotic now very common along the seacoast of Carolina and Georgia. 
Flowers July — October. 
