174 ORDER 70. COMPOSITE. 



orbiculiir. llecep. conical, chaffy. Cyp. 5, compressed, cohering with 2 con- 

 tiguous pales. American herbs with alternate leaves. (Flowers white.) 



1 P. integrifolium L. Pubescent, rigidly erect ; Ivs. lance-ovate, coarsely dentate- 

 crenate. coriaceous ; hds. many, corymbed. ~n Dry. Md., W. and S. 3 5f. Jl. Sept. 



i P. Hysteropliorns L. Puberulent, decumbent; Ivs. bipinnatifid. the upper lin- 

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



46. IV A, L. MARSH ELDER. HIOHWATER SHRUB. Hds. discoid, mo- 

 noecious. Invol. of 3 9 scales, distinct or partly united. Marginal fls 

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



linear, entire ; hds. axillary ; scales 5, distinct, rounded ; cypselse 5. Borders of sal\ 

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



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



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

 31. Iinbrlcaria Walt. ii Terete, glabrous ; Ivs. fleshy, linear-lanceolate. 3-veined, 

 sessilo : heads drooping, in leafy racemes ; scales 9, obtuse, imbricated in 2 rows, 

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



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

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

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

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

 opposite leaves and unsightly flowers. July Sept. Figs,. 73, 342. 



| 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, \ 



1 A. bldentata MX. nairy 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-aii- 

 gled. acutely pointed, the ribs produced into 4 short spines, fi) 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 below the conical top. (T) Along streams. &c. 5 lOf. Aug. 

 ft. integ-rifblia. Leaves ovate, acuminate, often some of them 3-lobed. 



3 A. artemlslaefolla L. Hog-weed? Lvs. twice-pinnatifld, smoothish, petioles cih 



ate ; sterile hds. in panicled racemes, fertile axillary, sessile, (I) Gardens, fields. 2-3f. 



4 A. psIlostachyaDC. Whitish, woolly, branching and leafy ; Ivs. rigid, the lower 



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



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

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

 chaffy. 5 Invol. clustered below, 2-lvd., clothed with hooked prickles, t- or 

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



1 X. Striiniarlum L. Rough, unarmed, branching; Ivs. cordate, lobed, 3-veined, un- 



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

 spreading, straight horns. Fields, way sir, e, N., M. 2 3f. Aug. Unsightly. 



2 X. spinosum L. Whitish-downy, armed with triple, slender, subaxillary spines ; 



Ivs. lance-ovate, 3-lobed, dentate, or entire ; 9 invol. oblong Waysides, &c. 2f. Sepi. 



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

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



