COMPOSITE. (COMPOSITE FAMILY.) 223 



toothed-margined; fertile flowers 2-4, the short corolla 5-parted. — Varies with 



smaller and fewer-flowered heads, and the corolla of the fertile flower truncate. 



— Drifting sands along the coast, Florida to North Carolina. Aug. and Sept. 



— Stem 1° -2° high. Leaves 1' long. 



36. AMBROSIA, Tourn. 



Heads monoecious, in racemes or spikes ; the upper ones sterile, nodding ; the 

 lower pistillate and fertile. Involucre of the sterile flowers hemispherical, com- 

 posed of 7-12 united scales, 5 - 20-flowered. Receptacle nuked or with slender 

 chaff. Corolla 5-toothed. Involucre of the fertile flowers 1 -flowered, ovoid or 

 turbinate, entire, closed, pointed, commonly with a row of tubercles or spines 

 near the apex. Corolla and stamens none. Achenia globose or ovoid. I'ap- 

 pus none. — Herbs. Leaves mostly pinnately lobed. Fertile flowers single or 

 clustered at the base of the sterile spike, or in the axils of the upper leaves, 

 bractcd. Flowers whitish. 



* Leaves undivided or 3 - 5-lol)ed, opposite : receptacle naked. 



1. A. triflda, L. Stem tall (6° -10°), 4-sided, rough-hairy ; leaves rough, 

 palmately 3 - 5-lobed, with the lobes ovate-lanceolate and serrate, or all undi- 

 vided ; fruit obovate, 6-toothed around the base of the conically beaked apex, 

 clustered. (A. integrifolia, MM.) — River-banks and rich soil, Florida and 

 northward. Aug. and Sept. 



* Leaves pinnately lobed ; the upper ones mostly alternate : receptacle commonly 



chaffy. 



2. A. crithmifolia, DC. Stem prostrate and shrubby at the base ; the 

 branches velvety pubescent ; leaves bipinnatifid, thickish, softly pubescent ; 

 spikes few, the terminal one elongated ; fruit downy, unarmed. — Sandy shores 

 at Key West, forming large clusters. 



3. A. artemisisefolia, L. Annual, erect, hairy or smoothish ; leaves bi- 

 pinnatifid, with linear lobes ; the upper often entire ; spikes single or panicled ; 

 fertile flowers single, clustered, or sometimes spiked ; fruit nearly globose, armed 

 with six short teeth. (A. elatior, L. A. paniculata, Michx., spines of the fruit 

 obsolete.) — Cultivated ground, everywhere. July- Sept. — Stem l°-4° high. 



4. A. hispida, Pursh. Hispid and hoary throughout ; leaves bipinnatifid, 

 with toothed lobes ; racemes terminal, somewhat panicled. — South Carolina, 

 Catesby. — Stem 1° high. Heads larger than in No. 1. (*) 



37. XANTHIUM, Tourn. Cocklebur. 



Heads monoecious, spiked ; the upper ones many-flowered, sterile, with the 

 scales of the involucre separate, in a single row ; the receptacle oblong, chaffy, 

 and the short corolla 5-toothed ; the lower ones fertile, consisting of two pistil- 

 late flowers, enclosed in a 2-celled oblong closed involucre, which is armed 

 externally with numerous hooked spines or bristles, and terminated by one 

 or two stout beaks. Corolla filiform. Achenium oblong, solitary in each cell. 

 — Coarse annual herbs. Leaves alternate, lobed and petioled. 



