COMPOSITE. (COMPOSITE FAMILY.) 273 



2. CYCLACELENA. Heads in pam'cled spikes, scarcely bracteate ; corolla 

 of the 5 fertile flowers a mere rudiment or none. 



3. I. xanthiifolia, Nutt. Annual, tall, roughish ; leaves nearly all oppo- 

 site, hoary with minute down, ovate, rhombic, or the lowest heart-shaped, doubly 

 or cut-toothed, or obscurely lobed ; heads small, crowded, in axillary and ter- 

 minal panicles. N. W. Wise, to Minn., Kan., and westward. 



43. AMBROSIA, Tourn. RAGWEED. 



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

 fertile 1-3 together and sessile in the axil of leaves or bracts, at the base of 

 the racemes or spikes of sterile heads. Sterile involucres flattish or top-shaped, 

 of 7 - 12 scales united into a cup, containing 5-20 funnel-form staminate flow- 

 ers, with slender chaff intermixed, or none. Anthers almost separate. Eertfte 

 involucre (fruit) oblong or top-shaped, closed, pointed, resembling an achene 

 (usually with 4-8 tubercles or horns near the top in one row), and enclosinga 

 single flower which consists of a pistil only ; the elongated style-branches pro- 

 truding. Achenes ovoid ; pappus none. Coarse homely weeds, with opposite 

 or alternate lobed or dissected leaves, and inconspicuous greenish flowers, in 

 late summer and autumn ; ours annuals, except the last. (The Greek and 

 later Latin name of several plants, as well as of the food of the gods.) 



1. Sterile heads sessile, in a dense spike, the top-shaped involucre extended on 

 one side into a large, lanceolate, hooded, bristly-hairy tooth or appendage; 

 fertile involucre oblong and 4-anf/led. 



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

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

 each side near the base ; fruit with 4 stout spines and a central beak. Prairies 

 of 111., Mo., and southward. 



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

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



2. A. trifida, L. (GREAT RAGWEED.) Stem stout (3-12 high), 

 rough-hairy, as are the large deeply 3-lobed leaves, the lobes oval-lanceolate 

 and serrate ; petioles margined ; fruit obovate, 5 - 6-ribbed and tubercled. 

 Var. iNTEGRirdLiA, Torr. & Gray, is only a smaller form, with the upper 

 leaves, or all of them, undivided, ovate or oval. Moist river-banks ; common. 



* * Leaves many of them alternate, all once or twice pinnatifid. 



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

 TER-WEED.) Much branched (1-3 high), hairy or roughish-pubescent ; 

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

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

 places everywhere. Extremely variable, with finely cut leaves, on the flower- 

 ing branches often undivided ; rarely the spikes bear all fertile heads. 



4. A. psilost&chya, 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 

 tubercles or with very small ones, pubescent. Prairies and plains, 111., Wise., 

 Minn., and southwest ward. Perennial, with slender running rootstocks. 



18 



