43. PARTHE'NIUM, L. (Gr. , a virgin; from its medicinal efficacy.) Heads many-flowered ; ray-flowers 5, somewhat ligulate, fertile; disk flowers tubular, sterile; involucre hemispherical, scales in 2 series, outer ovate, inner orbicular; receptacle conical, chaffy; achenia 5, compressed, cohering with 2 contiguous pales.- American herbs with alternate lvs.
1 P. integrifdlium L. St. pubescent, striate, erect; lvs. hispid-scabrous, lance-ovate, coarsely dentate-crenate. coriaceous, lower petiolate, upper sessile, hds. many, tomentous, corymbed. - Ц Dry soils, Mid. and W. States. St. rigid, 3 to of high. Radical petioles If long. Lvs. 4 to 12' long, 1/2 as wide. Hds. white, with 5 very short cucullate rays. Jl. - Sept 2 P. Hysterophorus L. Annual, puberulent, decumbent, lower lvs. bipinnatifid, upper linear; hds. numerous, very small, in a diffuse panicle. - River banks, Fla. to La.
44. I'VA, L. Marsh Elder. Highwater Shrub. Heads discoid, monoecious, involucre of 3 to 9 scales, distinct or partly united; marginal flowers 1 to 5, fertile, the others sterile; receptacle chaft'y; achenia obconic, obtuse ; pappus none. - Herbs or shrubs. Lower lvs. opposite.
1 I. frutesceus L. Shrubby; lvs. 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 opposite branches and lvs. Hds. small, green, drooping on short stalks, in leafy, paniculate racemes. Jl. - Sept.
2 I. ciliata Willd. Annual, hairy; lvs. ovate, acuminate, petiolate, coarsely toothed, upper lance-ovate; hds. spicate; scales 3, distinct, roundish, ciliate; adt. 3. - Wet grounds, I11. 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, like an Ambrosia. Aug. - Oct.
3 I. imbricaria Walt. Herbaceous, terete, glabrous; lvs. fleshy, linear-lanceolate, 3-nerved, tapering to the sessile base; hds. axillary; invol. 6 to 9, fleshy, obtuse, rounded scales in 2 rows, their margins scarious, lacerated; ach. 2 to 4 Ц 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. AMBRO'SIA, Tourn. Horse-weed. (Gr. , 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 0 ; styles 2 ; stamens 0. - Herbaceous plants with mostly opposite lvs. and unsightly flowers.
§ Sterile heads sessile , densely spicate, chaffy. Leaves alternate..........
§ Sterile heads pedicellate, racemed, not chaffy. - Leaves opposite....
- Leaves alternate...........
1 A. trifida L Hairy, rough; lvs. 3-lobed, serrate, the lobes oval-lanceolate, acuminate; fr. with 6 ribs ending below the conical summit. - (1) A very tall, herbaceous plant, along streams, etc. Can. and U. S., common. Stem 5 - l0f high, erect, branching, furrowed. 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.
ß. INTEGRIFOLIA. Lvs. ovate, acuminate, serrate, bristly on both sides, ciliato at base, often some of them 3-lobed. (A. integrifolia Muhl.)
2 A. artemisiaefdlia L. Hog-weed. Lvs. twice-pinnatifid, nearly smooth; petioles ciliate; rac. terminal, panicled; st. virgate. - (1) A common and troublesome weed of the gardens, fields, etc. (Can. to Ga.) far more worthy of its English than its Latin name. Stem 2 - 3f high, branching, pubescent when young. Leaves with segments acute and parallel, barren flowers small, green, in terminal racemes, the fertile ones sessile about the axils of the upper leaves. Aug., Sept (A. elatior Ph.)
3 A. psylostachya DC. Whitish with oppressed woolly hairs, branched; lvs. crowded, rigid, the lower opposite, bipinnatifid, upper lanceolate, sessile, pin-natifid; sterile hds. in spicate racemes, fertile clustered at the base of the sterila spikes, in the axils of the upper leaves; fr. hairy. - (J) Prairies, Wis. to Tex. Stem 1 - 5f high, at length very branching and leafy. Aug., Sept.
4 A. bidentata Mx. Very hirsute; st. branching; branches simple; lvs. crowded, mostly alternate, closely sessile or partly clasping, undivided, oblong, with a single tooth or short lobe on each side near the base; sterile hds. densely spicate, fertile axillary; fr.4 -angled, acutely pointed, the 4 ribs produced in 4 short spines. -(1) Prairies, I11. to La. Stem 1 - 3f high, with numerous leaves and very dense, terminal spikes. Jl. - Sept.
46. XAN'THIUM, Tourn. Clot-weed. Heads heterocephalous. Sterile, in globous heads ; scales distinct, in one row; anthers approximate, but distinct; receptacle chaffy. Fertile: involucre 2-leaved, clothed with hooked prickles, 1 or 2-beaked, enclosing 2 flowers; stamens 0. - (1) Coarse weeds with alternate Ivs.
1 X. Strumarium L. Rough, unarmed, branching; Ivs. cordate, lobed, 3-veined, unequally serrate; fr. elliptical, armed with uncinate, stiff thorns, and ending with 2, spreading, straight horns. - A coarse, rough plant, in old fields, etc. N. Eng. and Mid. States. Stem branched, bristly, spotted, 2 - 3f high. Leaves large, on long stalks, rigid. $ Fl3. few together, terminal, globular, green;♀ in sessile, axillary tufts. Fruit a hard, 2-celled burr, near an inch long, covered with stiff, hooked prickles, which, like those of the common burdock, serve to disperse the seeds. Aug. - Variable; fruit more than 1', or les3 than 1' in length ; thorns very close or somewhat scattered; horns spreading or incurved. (X. eehinatum Murray.)
2 X. apindsum L. Whitish-downy, armed with triple, slender, subaxillary spines, spines at base of the leaves triple, slender; Ivs. ovate-lanceolate, cuneate at base, petiolate, 3-lobed or dentate or entire, under surface and veins above whitish, twice longer than the spines; invol. oblong, with slender, uncinate thorns.- Roadsides and fields, Mass. to Penn. and Ga. Plant about If high, Very conspicuously armed with straw-colored spines 3/4 - 1' long. Heads sessile, sterile in the upper, fertile in the lower axils. Sept. - Nov.