430 AMBROSIACEAE. 



20-ribbed, somewhat narrowed at the base, truncate. Pappus of very copious 

 soft white simple capillary bristles, usually falling away connected, sometimes 

 with 1 or 2 stouter ones which fall separately. [The Greek name of the Sow- 

 thistle.] About 45 specie3, of the Old World. Type species: Sonchus 

 oleraceus L. 



1. Sonchus oleraceus L. Sp. PI. 794. 1753. 



Annual, with fibrous roots ; stem leafy below, nearly simple, 3-30 dm. 

 high. Basal and lower leaves petioled, lyrate-pinnatifid, 10-25 cm. long, the 

 terminal segment commonly large and triangular, the margins denticulate with 

 mucronate or scarcely spiny teeth; upper leaves pinnatifid, clasping by an 

 auricled or sagittate base ; uppermost leaves often lanceolate and entire ; 

 heads several or numerous, pale yellow, 18-30 mm. broad. 



Waste places and cultivated fields, Abaco, Great Bahama, the Biminis, New 

 Providence and Eleuthera to Acklin's Island and Grand Turk : Bermuda ; the 

 United States to continental tropical America ; West Indies. Naturalized from 

 Europe. SOW-THISTLE. 



2. LACTUCA L. Sp. PI. 795. 1753. 



Tall leafy herbs, with small panic-led heads of yellow, white or blue 

 flowers, and alternate leaves. Involucre cylindric, its bracts imbricated in 

 several series, the outer shorter, or of 1 or 2 series of principal nearly equal 

 inner bracts, and several rows of short outer ones. Receptacle flat, naked. 

 Rays tuncate and 5-toothed at the summit. Anthers sagittate at the base. 

 Style-branches mostly slender. Achenes oval, oblong or linear, flat, 3-5-ribbed 

 on each face, narrowed above or contracted into a narrow beak, which is some- 

 what expanded at the summit into a small disk bearing the copious soft 

 capillary, white or brown pappus-bristles. [The ancient Latin name, from lac, 

 milk, referring to the milky juice.] About 95 species, natives of the northern 

 hemisphere. Type species: Lactuca sativa L. 



1. Lactuca intybacea Jacq. Ic. Rar. 1: 16. pi. 162. 1786. 



Annual, glabrous; stem terete, simple and leafy below, paniculately 

 branched and nearly leafless above, 3-10 dm. high. Leaves thin, 0.5-2 dm. 

 long, nmcinate or irregularly lobed and toothed, the lower oblanceolate or 

 obovate, petioled, the upper lanceolate, acuminate, sessile and clasping; heads 

 solitary or in small clusters on the branches, distant, short-peduncled ; invo- 

 lucre narrowly cylindric, 10-12 mm. long, its outer bracts ovate or lanceolate, 

 broadly scarious-margined, much shorter than the linear acute inner ones; 

 rays yellow or white ; achenes linear, muricate, 3 mm. long ; pappus white, 

 plumose. 



Waste places and cultivated ground, Eleuthera, Cat Island, Conception Island, 

 Great Exuma, Long Island, Acklin's Island. Grand Turk. Inagua and Anguilla Isles : 

 Florida ; Cuba to Tortola and to Trinidad ; Jamaica ; Margarita ; Curagao ; Bonaire ; 

 Mexico to Venezuela. WILD LETTUCE. 



Family 5. AMBROSIACEAE Reichenb. 

 KAGWEED FAMILY. 



Herbs, monoecious, or sometimes dioecious, many of them weeds, rarely 

 shrubby, with alternate leaves, or the lower opposite, and small heads of 

 greenish or white flowers subtended by an involucre of few, separate or 



