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 l-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. Keceptacle naked 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. Pap- 

 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, 

 bracted. Flowers whitish. 



* Leaves undivided or 3 - 5-lobed, opposite : receptacle naked. 



1. A. trifida, 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, Muhl.) 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 1 - 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. XANTHIITM, 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. 



