328 coMPOSiTAE (composite family) 



§ 2. Sterile heads in single or panicled racemes or spikes, the involucre regular. 

 * Leaves opposite^ only once lobed; sterile involucre ^-ribbed on one side. 



2. A. trifida L. ' (Great R.) Stem stout, 1-6 m. high, rough-hairy, as are 

 the large deeply 8-lobed leaves, the lobes oval-lanceolate and serrate ; petioles 

 margined ; fruit obovoid, 6-(3-ribbed and tubercled. — Rich soil, common westw. 

 and south'w., much less so northeast w. Var. integrif6lia (Muhl.) T. & G. 

 Smaller, with the upper leaves (or all of them) undivided, ovate or oval. — Same 

 habitat, not rare. 



* * Leaves all once or tidce pinnatifid, many of them alternate. 



3. A. artemisiifblia L. (Romax Wormwood, Hog-weed, Bitter-weed.) 

 Much branched, 0.O-2.5 m. high, hairy or roughish-pubescent ; leaves thin, bi- 

 pinnatilid, smoothish above, paler or hoary beneath ; fruit obovoid or globular, 

 armed with about 6 short acute teeth or 873? nes. —Roadsides, etc., very common. 

 — Extremely variable, with finely cut leaves, those of the flowermg branches 

 often undivided ; rarely the spikes all fertile. 



4. A. psilostachya DC. Paniculately branched perennial, 5-lo dm. high, 

 with slender running rootstocks, rough and somewhat hoary with short stiffish 

 hairs ; leaves once pinnatijid^ thickish, the lobes acute, those of the lower leaves 

 often incised ; fruit obovoid, pubescent, the tubercles absent or smaZL — Prairies 

 and plains, 111. and Wise, to the Saskatchewan, westw. and southwestw. 



41. FRANSERIA Cav. 



Sterile and fertile heads separate as in Ambrosia, or sometimes mixed in the 

 inflorescence. Fertile involucre 1-4-celled, with a single pistil in each cell, 

 armed with spines in more than 1 series, bur-like. — Herbs (with us) or shrubs, 

 with mostly alternate leaves, flowering in late summer and autumn. (Named 

 for Antonio Franseri, Spanish botanist and contemporary of Cavanilles.) 

 Gaertneria Medic. 



1. F. tomentbsa Gray. Perennial, white icith sericeous tomentum; leaves 

 pinnately 3-7-parted ; segments lanceolate, mostly serrate, the basal ones small ; 

 sterile racemes 1-many ; spines of fertile involucre mostly uncinate-tipped. 

 (Gaertneria Ktze.) —Low ground. Neb., Kan., and Col. 



2. F. acanthicarpa (Hook.) Coville. Annual, hispid-hirsute, erect or diffuse, 

 loosely branched ; leaves bipinnatifid ; spines of the fertile involucre 4-5 mm. 

 long, stramineous, flattened, the tip usually straight. {Gaertneria Britton.) — 

 "Minn.," Sask., and southwestw. 



42. XANTHIUM [Tourn.] L. Cocklebur. Clotbur 



Sterile and fertile flowers in different heads, the latter clustered below, the 

 former in short spikes or racemes above. Sterile involucres and flowers as in 

 Ambrosia, but the bracts separate and receptacle cylindrical. Fertile involucre 

 coriaceous, ovoid or ellipsoid, clothed with hooked prickles so as to form a 

 rough bur, 2-celled, 2-flowered ; the flower consisting of a pistil and slender 

 thread-form corolla. Achenes oblong, flat. — Coarse annuals, with branching 

 stems, and alternate toothed or lobed petioled leaves ; flowering in summer and 

 autumn. (Greek name of some plant used to dye the hair ; from ^avObs, yellow.) 



JSf. ^. — The figures in this genus represent the mature fertile involucre x 1^. 



Leaves attenuate to both ends, with triple spines at base 1. X spinosum. 



Leaves cordate or ovate ; axils unarmed. 

 Body of mature bur fusiform-ellipsoid, more than twjce as long as thick. 

 Beaks of bur straight or nearly so ; prickles relatively few . . . . 2. X canadenae. 

 Beaks of bur incurved or hooked; prickles very numerous. 

 Prickles 3-6 mm. long, shorter than the diam'eter of the body . . . 3. X commune. 

 Pcickles 8-10 ram. long, exceeding the diameter of the body. 



Prickles crowded, weak, filiform, conspicuously hairy . . ■> . 4. X. speciosum. 

 Prickles more rigid, merely granular or obscurely puberulent . . 5. X ir)fl,exv,m. 

 Body of mature bur thick-ovoid. 'not more than twice as long as thick. 

 Prickles 8-10 ram. long, equaling or exceeding the diameter of the body . 4. X speciosum. 

 Prickles 3-5 (-7) mm. long, much shorter than the diameter of the body . 6. X. echinatum.. 



