AMBROSIACEAE. 



VOL. III. 



4. Iva ciliata Willd. Rough Marsh Elder. 

 Fig. 4123. 



Iva annua Michx. Fl. Bor. Am. 2 : 184. 1803. Not L. 

 Iva ciliata Willd. Sp. PI. &: 2386. 1804. 



Annual, hispid-pubescent; stem simple, or 

 branched, 2-6 high. Leaves nearly all oppo- 

 site, ovate, petioled, scarcely fleshy, puberulent 

 beneath, acuminate at the apex, abruptly or 

 gradually narrowed at the base, coarsely and ir- 

 regularly dentate, 3-nerved. the lower 4-5' long; 

 heads spicate-paniculate, about i" broad ; spikes 

 dense or interrupted, erect, 2'-8' long; upper 

 leaves linear-lanceolate, hispid, squarrose, much 

 longer than the heads; bracts of the involucre 

 3-5, distinct or united below, hispid; fertile flow- 

 ers 3-5, their corollas slender; staminate flowers 

 10-15. 



In moist soil, Illinois to Nebraska, south to Louisi- 

 ana and New Mexico. Plant with the aspect of an 

 Ambrosia. Aug.-Oct. 



5. Iva xanthiifolia Nutt. Burweed Marsh Elder. Fig. 4124. 



Iva xanthiifolia Nutt. Gen. 2: 185. 1818. 



Cyclachaena xanthiifolia Fresen. Ind. Sem. Hort. 

 Franc. 4. 1836. 



Annual ; stem much branched, pubescent or 

 puberulent above, glabrous below, 3-6 high. 

 Leaves nearly all opposite, broadly ovate, long- 

 petioled. acuminate at the apex, abruptly or 

 gradually contracted at the base, coarsely and 

 irregularly dentate, pale and canescent or pu- 

 berulent beneath, roughish above, 3-ribbed, the 

 lower often 6' long and wide; inflorescence 

 spicate-paniculate, terminal and axillary, ample, 

 naked; heads sessile or minutely peduncled, 

 l" broad or less; bracts of the involucre in 

 2 series of 5, the outer ovate, the inner obovate 

 or truncate, concave, subtending the usually 5 

 achenes; corollas of the fertile flowers rudi- 

 mentary or none; staminate flowers 10-15, their 

 corollas obconic. 



In moist soil, or sometimes in waste places, 

 Ontario to Assiniboia, south to Wisconsin, Ne- 

 braska, New Mexico and Utah. In waste grounds 

 farther east. Plant with the aspect of a Cheno- 

 podium. July-Sept. 



2. AMBROSIA [Tourn.] L. Sp. PI. 987. 1753. 



Monoecious (rarely dioecious) branching herbs, with alternate or opposite, mostly lobed 

 or divided leaves, and small heads of green flowers, the staminate spicate or racemose, the 

 pistillate solitary or clustered in the upper axils. Involucre of the pistillate heads globose- 

 ovoid or top-shaped, closed, i-flowered, usually armed with 4-8 tubercles or spines ; corolla 

 none; stamens none; style-branches filiform; achenes ovoid or obovoid; pappus none. Invo- 

 lucre of the staminate heads mostly hemispheric or saucer-shaped, 5-i2-lobed, open, many- 

 flowered; receptacle nearly flat, naked, or with filiform chaff; corolla funnelform, 5-toothed ; 

 anthers scarcely coherent, mucronate-tipped ; style undivided, penicillate at the summit. 

 [The ancient classical name.] 



About 15 species, mostly natives of America. Besides the following, some 5 others occur in 

 the southern and western United States. Type species: Ambrosia maritima L. 

 Sterile heads sessile; a lanceolate hispid lobe on inner border of involucre i. A. bidentata. 

 Sterile heads short-pedicelled, involucre depressed-hemispheric. 



Leaves opposite, palmately 3~5-lobed, or undivided ; receptacle naked. 2. A. trifida. 



Leaves opposite and alternate, i-2-pinnatifid ; receptacle chaffy. 



Annual ; leaves thin ; fruiting involucre spiny. 3. A. elatior. 



Perennial ; leaves thick ; fruiting involucre naked or tubercled. 4. A. psilostachya. 



