ORDER 70. COMPOSITE. 443 



5f high. Radical petioles If long. Lvs. 4 to 12' long, \ as wide. Hds. whifc^ 

 with 5 very short cucullate rays. Jl. Sept. 



2 P. Hysterophorus L. Annual, puberulent, decumbent, lower Ivs. bipinnatifid, 

 upper linear ; hda. numerous, very small, in a diffuse panicle. River banks, Fla. 

 to La. 



44. TVA, L. MARSH ELDER. HIGHWATER SHRUB. Heads dis- 

 coid, monoecious, involucre of 3 to 9 scales, distinct or partly united ; 

 marginal flowers 1 to 5, fertile, the others sterile ; receptacle chafty ; 

 achenia obconic, obtuse ; pappus none. Herbs or shrubs. Lower Ivs. 

 opposite. 



1 I. frutescens L. Shrubby; Ivs. fleshy, lanceolate, coarsely serrate; upper 

 lance-linear, entire ; hds. axillary ; scales 5, distinct, rounded ; ach. 5. Borders 

 of salt marshes, Mass, to Fla., common. St. 3 to 8f high, with numerous op- 

 posite branches and Ivs. Hds. small, green, drooping on short stalks, in leafy, 

 paniculate racemes. Jl. Sept. 



2 I. ciliata Willd. Annual, hairy; Ivs. ovate, acuminate, petiolate, coarsely 

 toothed, upper lance-ovate ; hds. spicate ; scales 3, distinct, roundish, ciliate; ach. 

 3. "Wet grounds, 111. to La. A coarse plant of no beauty, 3 to 7f high. Lvs, 

 3 to 4' long. Spikes dense, 3 to 5' long, numerous, panicled, green, liko an 

 Ambrosia. Aug. Oct. 



3 I. imbricaria "Walt. Herbaceous, terete, glabrous; Ivs. fleshy, linear-lanceo- 

 late, 3-nerved, tapering to the sessile base ; hds. axillary ; invol. of 6 to 9, fleshy, 

 obtuse, rounded scales in 2 rows, their margins scarious, lacerated ; ach. 2 to 4. 

 U Sea coast, N. Car. to Fla. Plant 1 to 2f high. Lvs. 1 to 2' long. Hds. 

 drooping, on short pedicels, in leafy clusters or racemes. Jl. Oct. 



45. AMBRCTSIA, Tourn. HORSE-WEED. (Gr. duflpooia, food of the 

 gods; a term strangely applied). Hds. heterocephalous. Sterile: 

 involucre of several scales united into a depressed, hemispherical cup, 

 many-flowered: anthers approximate, but distinct*, receptacle naked. 

 Fertile ; involucre 1 -leaved, entire or 5-toothed, 1 -flowered ; corolla 



; styles 2 ; stamens 0. Herbaceous plants with mostly opposite Ivs. 

 and unsightly flowers. 



Sterile beads sessile, densely spicate, chaffy. Leaves alternate No. 4 



Sterile heads pedicellate, racemed, not chaffy. Leaves opposite No. 1 



Leaves alternate Nos. 2, 3 



1 A. trifida L. Hairy, rough; Ivs. B-lobed, serrate, the lobes oval-lanceolate, 

 acuminate ; fr. with 6 ribs ending below the conical summit. CD A very tall, 

 herbaceous plant, along streams, &c. Can. and U.^}., common. Stem 5 lOf 

 high, erect, branching, farrowed. Leaves opposite, in 3 large, deep lobes, with 

 long points and close serratures. ' Flowers mean and obscure, in slender, leafless, 

 terminal racemes, the fertile in axillary glomerules. Aug. It is greedily eaten 

 by horses. 



(3. INTEGRIFOLIA. Lvs. ovate, acuminate, serrate, bristly on both sides, ciliato 

 at base, often some of them 3-lobed. (A. integrifolia Muhl.) 



2 A. artemisiaefolia L. HOG-WEED. Lvs. twice-pinnatifid, nearly smooth ; petioles 

 ciliate; rac. terminal, panicled; st. virgate. (> A common and troublesome 

 weed of the gardens, lields, &c. (Can. to Ga.) far more worthy of its Englisht 

 than its Latin name. Stem 2 3f high, branching, pubescent when young. 

 Leaves with segments acute and parallel. Barren flowers small, green, in ter- 

 minal racemes, the fertile ones sessile about the axils of the upper leaves. Aug., 

 Sept. (A. elatior Ph.) 



3 A. psylostachya DC. Wiitish with oppressed wooUy hairs, branched ; lys. 

 crowded, rigid, the lower opposite, bipinnatifid, upper lanceolate, sessile, pin- 

 natifid ; sterile hds. in spicate racemes, fertile clustered at the base of the sterile 

 spikes, in the axils of the upper leaves ; fr. hairy. Prairies, Wis. to Tex, 

 Stem 1 5f high, at length very branching and leafy. Aug., Sept. 



