174 ORDER 70. COMPOSITE. 



orbicular. Recep. conical, chaffy. Gyp. 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 dcntato- 



crenate, coriaceous ; hds. many, corymbed. 2* Dry. Md., W. and S. 3 5f. Jl. Sept. 



2 I*. Hysteropliorus L. Puberulent, decumbent ; Ivs. bipinnatifid, the upper lin- 



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



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

 nrcciou's. 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, tipper lance 



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

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



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



spicate ; sc. 3, distinct, roundish, ciliate ; cyp. 3. Wet. 111. to La. 3 7f. Aug. Oct. 



3 I. imbricaria Walt. 2f Terete, glabrous ; Ivs. fleshy, linear-lanceolate, 3-veined, 



sessile ; heads drooping, in leafy racemes ; scales G 9, 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, entire or 5- 

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

 opposite leaves and unsightly Howers. 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, 4 



1 A. bld.enta.ta 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 ; IV. 4-au- 

 jfled, acutely pointed, the ribs produced into 4 short spines. 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. 

 /3. inteffri folia. Leaves ovate, acuminate, often some of them 3-lobed. 



3 A. artemislaefolia L. Hog-weed. Lvs. twice-pinnatifid, smoothish, petioles cili 



ate ; sterile hds. in panicled racemes, fertile axillary, sessile. Gardens, fields. 2-Sf. 



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



opp., bipinnatifid, upper pinuatifid ; 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 with alternate leaves. 



1 X. Strumarinm 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, ways!ae$, 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 ; ? invol. oblong Waysides, &c. 2f. Sept. 



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

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



