THISTLE FAMILY 629 
usually lobed or deeply divided and with inconspicuous greenish heads of 
flowers, the stamens and pistils occupying different heads. The staminate 
heads have an involucre of several scales, united to form a cup in which 
are from 5 to 20 staminate flowers on a chaffy receptacle. The pistillate 
heads have each a single flower, consisting only of a pistil, surrounded 
by an involucre of one piece. There is no aigrette or other indication of 
a calyx. 
l. A. trifida, L. (Fig. 2, pl. 168.) Great Racweep. Tall herb, 3 
to 17 ft. high, hairy or nearly smooth. Leaves opposite, 3-lobed, the lobes. 
oval-lance-shaped. Moist soil. July-Oct. 
2. A. artemisiaefolia, L. (Fig. 1, pl. 168.) Racwrrp. Leaves lobed 
on each side of the midvein (pinnate). Stem 1 to 6 ft. high. A common 
and troublesome weed in waste places. July-Oct. 
3. XANTHIUM, L. 
Coarse, rough and spiny herbs, with alternate, lobed or conspicuously 
dentate leaves and small flowers, the pistillate in bur-like heads with 
hooked prickles, the staminate in rounded heads with a short involucre. 
1. X. spinosum, L. (Fig. 4, pl. 168.) Spiny CiotwereEp. Leaves 
lance-shaped, deeply lobed on each side of the midvein, under surface and 
veins above white, at the base of the leaf about three long stiff prickles. 
Staminate heads above at extremity of branches, fertile heads prickly, 
in the axils below. Waste grounds. Aug.-Nov. 
2. X. strumarium, L. (Fig. 5, pl. 168.) Burwerep. Branching, 1 to 
6 ft. high, not armed with prickles at the leaves. Leaves in general out- 
line rounded and somewhat triangular, with deep lobes, the borders toothed, 
heart-shaped at base. Fruit elliptic, armed with stiff prickles and ending 
with two straight or slightly curved horns. Waste places. (Is perhaps 
only a variety of X. canadense.) <Aug.-Oct. 
3. XX. canadense, Mill. (Fig. 6, pl. 168.) HrepcreHoa BuRwEED. 
Resembles above, but bur much longer and the two horns are curved in and 
the extremity is not divided. Waste places, river banks, ete. Aug.-Oct. 
4. X. commune, Britton. Common CLorweeEp. Leaves broadly egg- 
shaped, more or less lobed. Burs commonly solitary in the axils; prickles 
slender, hooked at tip and hispid. Northern New York, and westward. 
Famity V.—COMPOSITAE. THISTLE FAMILY 
This is by far the largest family of flowering plants. In the 
North Eastern United States the plants are nearly all herbs; but 
in tropical climates some members of the family are trees. The 
flowers are associated in heads which have the appearance of a 
single flower, as, for example, the daisy or the aster, in which many 
small yellowish flowers—florets—are gathered at the center of a 
group while in nearly all cases a single row of white or colored 
flowers of a different kind are arranged in a single row about the 
margin. The groups are subtended by an involucre of bracts which 
