COMPOSITAE (COMPOSITE FAMILY) 541 



tending the fertile flowers, or these wanting in staminate heads. Receptacular 

 bracts few, narrow. Pistillate flowers 1 or 2, destitute of corolla; staminate 

 flowers 6-12, the filaments almost free from the corolla and monadelphous 

 up to the lightly connected anthers. Achenes surpassing the outer involucre, 

 convex on the dorsal side, flat on the anterior face, conspicuously margined 

 with a scarious pectinate border. Pappus of several small squamellae. 



1. Dicoria Brandegei Gray, Proc. Am. Acad. 11: 76. 1875. Strigillose- 

 canescent, diffusely and alternately branched: leaves of the branches oblong- 

 lanceolate or partly spatulate, obtuse, mostly entire, 2-3 cm. long, and with 

 slender petiole: heads sparse, racemose-paniculate: fertile flower solitary; the 

 dilated-cuneate hyaline subtending bract hardly surpassing the outer invo- 

 lucre: achene naked and exserted, bordered with pectinate callous teeth 

 connected by an indistinct scarious margin. Sandy bottoms of the San Juan, 

 Colorado. 



42. AMBROSIA L. RAGWEED 



Coarse herbs with mostly lobed or dissected opposite and alternate leaves 

 and dull inconspicuous flowers. Sterile heads racemose or spicate and with no 

 bracts; fertile flowers usually glomerate in axils below. Involucre of the 

 staminate flowers depressed-hemispherical to turbinate, 5-12-lobed or trun- 

 cate, herbaceous. Receptacle flat or flattish, usually with some filiform chaff 

 among the outer flowers. Involucre of the solitary fertile flower nutlike, apicu- 

 late or beaked at the apex, and usually armed with 4-8 tubercles or short 

 spines in a single series below the beak. 



Leaves entire or palmately 3-cleft; involucre of staminate heads 



3-4-ribbed . . f 1. A. trifida. 



Leaves once to thrice pinnatifid; involucres of staminate flowers not 

 ribbed. 



Annual; fruit with acute teeth 2. A. artemisiaefolia. 



Perennial from rootstocks; fruit unarmed or with blunt teeth . 3. A. psilostachya. 



1. Ambrosia trifida L. Sp. PL 987. 1753. Tall and stout, 1-3 m. high, 

 roughish-hispid or almost glabrous: leaves all opposite, very deeply 3-lobed or 

 the lower 5-lobed; the lobes acuminate, serrate: sterile racemes long and dense; 

 fertile heads clustered and as if involucrate by short bracts: fruit very thick, 

 with 5-7 strong ribs or angles terminating above in spinous tubercles around 

 the base of the conical beak. Var. integrifolia T. & G. with entire leaves. 

 GREAT RAGWEED. Moist banks and draws; Colorado and far northward and 

 eastward. 



2. Ambrosia artemisiaefolia L. 1. c. Variously pubescent or hirsute, panic- 

 ulately branched, 3-6 dm. high, or taller: leaves thinnish, bipinnatifid or 

 pinnately parted, with the divisions irregularly pinnatifid or sometimes nearly 

 entire, on the flowering branches often undivided: sterile heads pediceled: 

 fruit short-beaked, armed with 4-6 short acute teeth or spines. A weed in 

 waste and cultivated grounds across the continent, known variously as 

 ROMAN WORMWOOD, RAGWEED, and BITTERWEED. 



3. Ambrosia psilostachya DC. Prodr. 5: 526. 1836. Stems simple, erect, 

 commonly 5-10 (2-15) dm. high from slender running rootstocks; herbage 

 scabrous or short-hirsute, somewhat strigose: leaves once or the lower twice 

 pinnatifid, with acute lobes: fruit an obovoid turgid bur, about 3 mm. long, 

 mostly solitary in the axils, pubescent, rugose-reticulated, bearing 4 pro- 

 tuberances or sometimes unarmed. WESTERN RAGWEED. A common weed 

 along roadsides and in waste places throughout western North America. 



43. FRANSERIA Cav. 



Ours are herbaceous, with chiefly alternate leaves, and the spines of the 

 fruiting and 1-2-flowered involucre comparatively few. Heads of staminate 

 flowers as in A rnbrosia. or sometimes intermixed with the pistillate. Fertile 

 involucre 1-4-flowered, 1-4-celled, a single pistil to each cell, 1-4-rostrate, 



