COMPOSITE. 185 



Old fields. Can. to Flor. Aug., Sept. (T).~Stem 14 feet high, usually 

 rough. Heads small ; the sterile ones in long slender paniculate racemes. Fruit 

 solitary or in small clusters at the base of the sterile racemes, armed with about 

 6 short acute teeth. A troublesome weed. Hog-weed. 



4. A. paniculata Mich. : stem branching, paniculate at the summit, and 

 with the petioles villous ; leaves green on both sides, bi-pinnatifid, the seg- 

 ments lanceolate ; fruit somewhat clustered, small, obovate, slightly awned. 

 Iva monophylla Walt. 



Old fields. Can. to Flor. July Sept. (T). Pursh.Stem 24 feet high. 

 Heads in simple terminal and axillary racemes. Paniculate Rag-weed. 



5. A. heterophylla Muhl. : stem pubescent or villous, paniculate ; cauline 

 leaves pinnatifid, subdentate, petiolate ; those of the branches lanceolate, 

 sessile; petioles with long cUiae ; racemes terminal, solitary. A. Peruviana 



wnu. 



Banks of streams. Penn. July Sept . Muhl Fruit with 5 6 acute 

 teeth below the summit. Perhaps this and the preceding are only varieties of 

 A. artimisi&folia. Various-leaved Rag-weed. 



29. IVA. Linn. Marsh Elder. 



(Origin of the name doubtful.) 



Heads monoecious, not radiate. Fertile flowers 1 5, mar- 

 ginal, with a small tubular corolla. Sterile flowers numerous, 

 with a tubular -campanulate corolla. Scales of the involucre 

 3 5 in a single series, or 6 9 and imbricated. Receptacle 

 small, chaffy. Achenia obovoid, somewhat compressed. Pap- 

 pus none. 



/. frutescens Linn. : shrubby, smooth ; leaves opposite, oval or oval-lan- 

 ceolate, somewhat petioled, deeply-serrate, slightly scabrous ; uppermost 

 linear-lanceolate, entire ; heads axillary, depressed-globose, pedicellate j 

 scales of the involucre 5, orbicular. 



Sea coast. Mass, to Flor. Aug., Sept. T^. Stem 3 8 feet high, much 

 branched. Leaves thick and somewhat fleshy. Heads numerous, small, green- 

 ish, in axillary leafy racemes, forming a large terminal panicle. 



Marsh Elder. Highwater Shrub. 



30. HELIOPSIS. Pers. Ox-eye. 



(From the Greek /A>J, the sun, and oi^is, appearance; in allusion to the form 

 of the heads of flowers. ) 



Heads many-flowered ; the ray flowers in one series, ligulate, 

 fertile ; those of the disk tubular, perfect. Involucre in 2 3 

 series ; the outer scales leafy, the rest imbricate. Receptacle 

 conic. Achenia angular, partly surrounded by the chaff. 



H. IfBvis Pers. : stem smooth ; leaves smoothish, ovate-lanceolate or ob- 

 long-ovate, tapering at base into a petiole, serrate, 3- nerved. Helianthus 

 Icevis Linn. 



Banks of streams Throughout the IT. S. Aug., Sept. 1\.. Stem 24 feet 



