292 COMPOSITtE. Ambrosia. 



larger : involucre minutely hispid. Chaff of the receptacle filiform. Mature 

 fruit twice as larije as in A. artemisiaefolia, pubescent towards the summit, 

 obscurely triangular at the base, entirely destitute of teeth or horns. 



5. A. longistylis (Nutt.) : annual, scabrous ; stem (apparently) simple ; 

 leaves pinnatifid; the segments oblong-linear; bracts em ire ; fertile Howers 

 axillary, conglomerate, with exceedingly long styles; fruit cornute, spiny at 

 the summit ; sterile flowers about 30, in a slightly toothed involucre ; the 

 receptacle iiliformly paleaceous ; cusps of the anthers filiform. Nutt.! in 

 trans. Amer. j}hil. soc. I. c. p. 344. 



Rocky Mountains : allied to Franseria, Nuttall! — Plant strigose-hispid. 



§ 2. Sterile heads closely sessile, densely aggregated in a cylindrical sessile 

 spike terminating the stem or branches ; the involucre turbinate, truncate, 

 the inner margin produced into a long and consjncuous lanceolate, hispid,, 

 decurved or cucullate tooth or appendage : receptacle chaffy: fruit (fertile 

 involucre) oblong, 4.-angled and sometchat prismatic, solitary or clustered in 

 the axils of the lanceolate closely sessile 1-nerved leaves. — Cercomeris. 



6. A. hidcntata (Michx.) : annual ; stem hirsute with spreading hairs ; the 

 branches simple ; leaves very numerous, mostly alternate, hirsute or hispid, 

 partly clasping, commonly with a short spreading lobe or broad tooth on each 

 side near the" base, entire above, or rarely remotely serrate, acute ; sterile 

 spike squarrose with the recurved very hispid appendage of the involucres; 

 receptacle small, about 10-flowered; the filiform scarious chaft' much shorter 

 than the corolla ; fruit acutely pointed ; the 4 angles or ribs terminating in 

 short acute spines.— ili/fZ/.r. / jl 2. p. 182 : Pursh, Ji. 2. p. 581. 



Prairies of Illinois ! Missouri ! Arkansas ! and Louisiana ! July-Sept. — 

 Stem 1-3 feet high. Leaves 1-2 inches long. Sterile spikes very dense ; 

 the appendages of the involucres, which are twice or thrice the length of the 

 involucre itself appearing like recurved bracts. Fertile heads numerous, 

 minutely pubescent, when mature about 4 lines long, including the rigid 

 and sharp terminal horn or cusp. Achenium conformed to the cavity of the 

 involucre. 



X Doubtful Species. 



7. A.Mspida{'P\xxs\i): canescent-hispid throughout; leaves bipinnatifid, 

 the segments incised ; racemes terminal, somewhat paniculate. Pursh, ji. 

 \suppl) 2. p. 743. 



South Carolina, Catesby {Herb. Sherard.) About a foot high: flowers 

 larger than in A. trifida. Pursh. 



8. A. tomentosa (Nutt.) : perennial ; stem low ; leaves bipinnatifid, the 

 lower side white and tomentose; spikes solitary. Nutt. gen. 2. p. 186 



Upper Missouri : rare ; 1-2 feet high. Nuttall. 



81. FRANSERIA. Cav. ic. 2. t. 200 ; Willd. hort. Berol. t. 2 ; DC. 



Sterile heads occupying the upper portion, the fertile the base of the ra- 

 cemes or spikes. Sterile Fl. Involucre hemispherical, composed of 

 8-12 united scales, 15-20-flowered. Receptacle flatlish, chaffy ; the chaff 

 filiform. Corolla infundibuliform, 4-5-toothcd. Anthers tipped with a mu- 

 cronate-setigerous inflexed appendage. Ovary none : abortive style included, 



