212 COMPOSITE. (COMPOSITE FAMILY.) 



sected leaves, and inconspicuous greenish or whitish flowers. ('A/x/Spotria, th 

 food of the gods, an ill-chosen name for these worthless and coarse weeds.) 



1. Sterile heads sessile, crowded in a dense cylindrical spike, the top-shaped involucre 

 with the truncate margin extended on one side into a large, lanceolate, hooded, 

 recurved, bristly-hairy tooth or appendage ; fertile involucre oblong and 1-angled. 



1. A. bidentata, Michx. Hairy (l-3 high), very leafy; leaves al- 

 ternate, lanceolate, partly clasping, nearly entire, except a short lobe or tooth 

 on each side near the base. Prairies of Illinois and southward. Aug. 



2. Sterile heads in single or panicled racemes or spikes, the involucre regular. 

 * Leaves opposite, only lobed: sterile involucre 3-ribbed on one side. 



2. A. trifida, L. (GREAT RAGWEED.) Stem square, stout (4 -12 

 high), rough-hairy, as are the large deeply 3-lobed leaves, the lobes oval-lanceo- 

 late and serrate ; petioles margined ; fruit obovate, 6-ribbed and tubercled. (J) 

 Var. INTEGRIF6LIA is only a smaller form, with the upper leaves or all of 

 them undivided, ovate or oval. Moist river-banks ; common. Aug. 



* # Leaves many of them alternate, once or twice pinnatiftd. 



3. A. artemisiae folia, L. (ROMAN WORMWOOD. HOG-WEED. BIT- 

 TER-WEED.) Much branched (l-3 high), hairy or roughish-pubescent ; 

 leaves thin, twice-pinnatifid, smoothish above, paler or hoary beneath ; fruit obo- 

 void or globular, armed with about 6 short acute teeth or spines. Waste 

 places everywhere. July -Sept. An extremely variable weed, with finely 

 cut leaves, embracing several nominal species. 



4. A. psilostachya, DC. Paniculate-branched (2 -5 high), rough 

 and somewhat hoary with short hispid hairs ; leaves once pinnatifid, thickish, the 

 lobes acute, those of the lower leaves often incised ; fruit obovoid, without tuber- 

 cles or with very small ones, pubescent. Q) (A. coronopifolia, Torr. Sf Gr.) - 

 Prairies and plains, Illinois and southwestward. Aug. 



31. XANTHIUM, Tourn. COCKLEBUR. CLOTBUR. 



Sterile and fertile flowers occupying different heads on the same plant ; the 

 latter clustered below, the former in short spikes or racemes above. Sterile 

 involucres and flowers as in Ambrosia, but the scales separate. Fertile invo- 

 lucre closed, coriaceous, ovoid or oblong, clothed with hooked prickles so as to 

 form a rough bur, 2-celled, 2-flowered ; the flowers consisting of a pistil with a 

 slender thread-form corolla. Achenia oblong, flat ; destitute of pappus. 

 Coarse and vile weeds, with annual roots, low and branching stout stems, and 

 alternate toothed or lobed petioled leaves. (Name from dv6os, yettow, in allu 

 sion to the color the plants are said to yield.) 



1. X. Strumaritim, L. (COMMON COCKLEBUR.) Rough; stems un- 

 armed; leaves dilated-triangular and more or less heart-shaped, on long petioles, 

 toothed and cut or obscurely lobed; fruit oval or oblong ('-' long), pubes- 

 cent on the lower part of and between the hooked prickles, and with two strong 

 and usually straight beaks at the summit. Barn-yards, &c. (Nat. from Eu ) 

 Varies into forms with more spotted stems, and often larger fruit ('-!' long), 



