174 ORDER 70, COM POSIT.fi. 



orbicular. Ileccp. conical, chaff}'. Cyp. 5, compressed, cohering with 2 con- 

 tiguous pales. American herbs with alternate leaves. (Flowers w T hite.) 

 1 P. integrifollum L. Pubescent, rigidly erect; Ivs. lanre-ovato, coarsely dentato- 

 crenate, coriaceous ; hds. many, corymbed. TX Dry. Md.,W. andS. 3 5f. Jl. Sept. 

 JJ P Hysteropliorus L. ' Pnberulent, decumbent ; Ivs. bipinnatifid. the tipper lin- 

 ear ; heads numerous, very email, in a diffuse panicle. River banks, Fla. to La. 



46. IV A, L. MARSH ELDER. HIGHWATER SHRUB. lids, discoid, mo- 

 nrecious. Invol. of 3 9 scales, distinct or partly united. Marginal fis. 

 1 5, fertile, the others sterile. Recep. chaffy. Cyp. obconic, obtuse. Pap. 

 none. Herbs or shrubs. Lower Ivs. opposite. Hds. small, greenish white 



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



linear, entire ; hds. Axillary ; scales 5, distinct, rounded ; cypselae 5. Borders of salV 

 marshes. Mass, to Fla. 3 Sf. bushy. Racemes paniculate, hds. drooping. July Sept, 



2 I. clllata Willd. Annual, hairy ; Ivs. lance-ovate, acuminate, coarsely toothed ; hds. 



spicate ; BC. 3, distinct, roundish, ciliate ; cyp. 3. Wet, HI. to La. 3 7f. Aug. Oct. 



3 I. imbrlcaria Walt. y. Terete, glabrous ; Ivs. fleshy, linear-lanceolate. 3-veined, 



sessile ; heads drooping, in leafy racemes ; scales 6 0, obtuse, imbricated in 2 rows, 

 with torn edges. Sea-coast, S. 1 2f. 



47. AMBROSIA, Touru. HORSE-WEED. Monoecious. Sterile involucre 

 of several scales united into a depressed, hemispherical cup, many-flowered. 

 Anth. approximate, but distinct. Fertile involucre 1-leaved, en tire, or 5- 

 toothed, 1 -flowered. Cor. 0. Sty. 2. Sta. 0. Herbaceous plants with mostly 

 opposite leaves and unsightly flowers. July Sept. Figs. 73, 343. 



Sterile heads sessile, densely spicate, chaffy. Leaves alternate .No. 1 



Sterile heads pedicellate, racemed, not chaffy. a Leaves opposite No. 2 



a Leaves alternate Nos. 3, 4 



1 A. btdentata MX. Hairy and leafy, with simple branches ; Ivs. sessile or clasping, 



oblong, with a single tooth on each side near the base; fertile hds. axillary; fr. 4-an- 

 gled, acutely pointed, the ribs produced into 4 short spines. (T) Prairies, 111. to La. l-3f. 



2 A. trifida L. Rough-hairy; Ivs. 3-lobed, serrate, lobes oval-lanceolate, acuminate ; 



fr. with 6 ribs ending bflow the conical top. Along streams, &c. 5 lOf. Aug. 

 /3. integri folia. Leaves ovate, acuminate, often eomc of them 3-lobed. 



3 A. artemisiaelolia L. Hog-tceed. Lvs. twice-pinnatifid, smoothish, petioles cih 



ate; sterile hds. in panicled racemes, fertile axillary, sessile. (!) Garden*, fields. 2-3f 



4 A. psllostuchya DC. Whitish, woolly, branching and leafy : Ivs. rigid, the lower 



opp., bipinnatifid, upper pinnatifid ; rac. spike-like ; fr. hairy. (T) Prairies. Wis. to Tex. 



48. XANTHIUM, Tourn. CLOT-WEED. Monoecious. & Hds. spicate 

 above. Scales distinct, in one row. Anth. approximate, but distinct. Recep. 

 chaffy. ? Invol. clustered below, 2-lvd., clothed with hooked prickles, 1- or 

 2 -beaked, enclosing 2 fls. Sta, 0. (i) Coarse weeds wjth alternate leaves. 



1 X. Sti*uma.rium L. Rough, unarmed, branching; Ivs. cordate, lobed, 3-veincd. un- 



equally serrate : fruit elliptical, armed with stiff, hooked thorns, and ending with 2 

 spreading, straight horns. Fields, waysiies, N.. M. 2 3f. Aug. Unsightly. 



2 X. spinosuiu L. Whitish-downy, armed with triple, slender, subaxiliary spines ; 



Ivs. lance-ovate, 3-lobed, dentate, or entire ; ? invol. oblong Waysides, &c. 2f. Sept. 



49. MELANTHERA, Cass. Fls. all tubular, $ . Scales in 2 subequnl 

 series. Kecep. chatty, the pales partly investing the fls. Cyp. short, truncate, 



