250 COMPOSITE. (COMPOSITE FAMILY.) 



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 irapBevos, virgin.) 



1. P. integrifdlium, L. Rough-pubescent perennial (l-3 high); 

 leaves oblong or ovate, crenate-toothed, or the lower (3' -6' long) cut-lobed be- 

 low the middle ; heads many in a very dense flat corymb. Dry soil, Maryland 

 to Wisconsin and southward. June -Aug. 



29. I V 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 or no corolla ; the latter with a funnel-form 5-toothed corolla. 

 Anthers nearly separate. 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 of flowers ; in summer and au- 

 tumn. (Name of unknown derivation.) 



1. Fertile flowers with a small tabular corolla: involucre simple (heads nodding in 

 the axils of leaf -I ike bracts, forming spikes or racemes). 



1. I. frilt6scens, L. Shrubby at the base, nearly smooth (3 -8 high); 

 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, in leafy 

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

 coast of Massachusetts to Virginia, and southward. 



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

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

 spikes, with conspicuous ovate-lanceolate rough-ciliate bracts ; scales of the in- 

 volucre and fertile flowers 3-5. Moist ground, from Illinois southward. 



2. EUPHR6SYNE, DC. Fertile flowers 5, in the axils of as many thin mem- 

 branaceous scales of the involucre, which loosely enwrap the achenia, their corolla 

 a mere rudimentary ring or none. 



3. I. xanthiifblia, Nutt. Annual., tall, roughish ; leaves nearly all oppo- 

 site, hoary with minute down, ovate, rhombic, or the lowest heart-shaped, doubly 

 or cut-toothed, or obscurely lobed ; heads small, crowded in spikes or clusters 

 disposed in axillary and terminal panicles ; bracts inconspicuous. N. W. Wis- 

 consin (T. J. Hale), and northwestward. 



30. 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 the 

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

 composed of 7-12 scales united into a cup, containing 5-20 funnel-form stain- 



