COMPOSITE. (composite FAMILY.) 273 



§ 2. CYCLACH.^NA. Heads in pon'cled spike.s, scarce! 1/ hractente ; corolla 

 of the 5 fertile Jlowers a mere nulinunl or none. 

 3. I. xanthiifblia, Nutt. Annual, tall, roughlsh ; leaves nearly all oppo- 

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

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

 minal panicles. — N. W. ^^'isc. to Minn., Kan., and westward. 



43. AMBROSIA, Tuurn. Ragweed. 



Stei'ile and fertile flowers occupyinj^ 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 How- 

 ers, witli slender chaff intermixed, or none. Anthers almost separate. Fertile 

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

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

 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-angled. 



1. A. bident^ta, 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. ixtegrif6lia, 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 pinnatifd. 



3. A. artemisisefblia, 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 irith 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 iiairs; leaves once pinnatijid, ihickish, the 

 lobes acute, those of the lower leaves often incised ; fruit obovoid, ivithout 

 tubercles or with very small ones, ])ubescent. — Prairies and plains, 111., Wise, 

 Minn., and south westward. Perennial, with slender running rootstocks. 



18 



