COMPOSITE. (COMPOSITE FAMILY.) 211 



28. PARTHEN1UM, L. PARTHENUJM. 



Heads many-flowered, inconspicuously radiate ; the 5 ray-flowers with very 

 short and broad obcordate ligules not projecting beyond the woolly disk, pistil- 

 late and fertile ; the disk-flowers staminate with imperfect styles, sterile. Invo- 

 lucre hemispherical, of 2 ranks of short ovate or roundish scales. Receptacle 

 conical, chaffy. Achenia only in the ray, obcompressed, surrounded by a slen- 

 der callous margin, crowned with the persistent ray-corolla and a pappus of 2 

 small chaffy scales. Leaves alternate. Heads small, corymbed; the flowers 

 whitish. (An ancient name of some plant, from napdevos, virgin.) 



1. P. in te^ri folium, L. Rough-pubescent (l-3high); leaves ob- 

 long or ovate, crenate-toothed, or the lower (3 r - 6' long) cut-lobed below the 

 middle ; heads many, in a dense flat corymb. \ Dry soil, Maryland to Wis- 

 consin, and southward. 



29. IV A, L. MARSH ELDER. HIGHWATER-SHRUB. 



Heads several-flowered, not radiate; the pistillate fertile and the staminate 

 sterile flowers in the same heads, the former few (1-5) and marginal, with a 

 small tubular corolla ; the latter with a funnel-form 5-toothed corolla. Scales 

 of the involucre few, roundish. Receptacle small, with narrow chaff among 

 the flowers. Achenia obovoid or lenticular. Pappus none. Herbaceous or 

 shrubby coarse plants, with thickish leaves, the lower opposite, and small 

 greenish-white heads on short recurved peduncles in the axils of the leaves or 

 of bracts. (Derivation unknown.) 



1. I. frutescens, L. Shrubby at the base, nearly smooth (3 -8 high) j 

 leaves oval or lanceolate, coarsely and sharply toothed, rather fleshy, the upper 

 reduced to linear bracts, in the axils of which the heads are disposed, forming 

 leafy panicled racemes ; fertile flowers and scales of the involucre 5. Salt 

 marshes, coast of Massachusetts to Virginia, and southward. Aug. 



2. I. Cilmta, Willd. Annual (2 -8 high) , rough and hairy; leaves ovate, 

 pointed, coarsely toothed, downy beneath, on slender dilate petioles ; heads in dense 

 panicled spikes, with conspicuous ovate-lanceolate rough-ciliate bracts ; scales 

 of the involucre and fertile flowers 3-5. Moist ground, from Illinois south- 

 ward. Aug. - Oct. 



3O. AMBROSIA, Tourn. RAGWEED. 



Sterile and fertile flowers occupying different heads on the same plant ; the 

 fertile 1-3 together and sessile in the axil of leaves or bracts, at the base of tho 

 racemes or spikes of sterile heads. Sterile involucres flattish or top-shaped, 

 composed of 7 - 1 2 scales united into a cup, containing 5-20 funnel-form stami- 

 nate flowers ; with slender chaff intermixed, or none. Fertile involucre (fruit) 

 oblong or top-shaped, closed, pointed, and usually with 4-8 tubercles or horns 

 near the top in one row, enclosing a single flower which is composed of a pistil 

 only ; the elongated branches of the style protruding. Achenia ovoid : pappus 

 none. Chiefly annual coarse weeds, with opposite or alternate Ic bed or d is 



