COiMPOSLTAE (C( )iyrPOSITE kamily) 827 



* * Stem-leaves auriculate-clanping. 



3. P. auriculktum Britton. Eootstook very thick and tuber-like ; stem l-? 

 dm. liigh, villous ; some of the leaves pinnatifid at base, pubescent on the veins 

 beneath with conspicuous appressed strongly divergent hairs. — Mis. of Va. 



39. IVA L. Marsh Elder. Highwater-siikub 



Heads several-flowered, not radiate ; pistillate and staminate flowers in the 

 same heads, the former few and marginal. Anthers nearly separate. Bracts 

 of the involucre few, roundish. Receptacle small, with narrow chaff among the 

 flowers. Aohenes obovoid or lenticular ; pappus none. — Herbaceous or shrubby 

 coarse plants, with thickish leaves (the lower opposite) and small nodding 

 greenish-white heads of flowers ; in summer and autumn. (Name of unknown 

 derivation.) 



§ 1. EUIVA Hoffm. Heads spicate or racemose in the axils of leaves or leaf- 

 like bracts ; fertile Jloioers with evident corolla. 



1. I. orllria Bartlett. Shruhliy at base, nearly smooth, 5-10 dm. high; leaves 

 oval or lanceolate, coarselij and sharply toothed, fleshy, the upper reduced to 

 linear bracts, in the axils of which the heads (5-6 mm. in diameter) are disposed 

 in leafy panicled racemes ; fertile flowers and bracts of involucre 6. {I.frutes- 

 cens Man. ed. 6, not L.) — Salt marshes, coast of Mass. to Md. 



2. I. imbricata Walt. Suffruticose, glabrous, simple, 3-6 dm. high ; leaves 

 alternate, fleshy, spatulate-oblong or lanceolate, entire or slightly serrate ; heads 

 6-8 mm. high; hemispherical involucre of 0-9 bracts, the outer orbicular. — 

 Sandy coast, Va., and southw. 



3. t. iili^ta Willd. Annual, 3-6 dm. high, rough and hairy ; leaves ovate, 

 pointed, coarsely toothed, downy beneath, on slender ciliale petioles; heads in 

 dense spikes, with conspicuous ovate-lanceolate rough-ciliate bracts ; bracts of 

 the involucre and fertile flowers 3-5. — Moist ground, 111. to Neb., and southw.; 

 occasionally on dumps, etc., eastw. 



§ 2. CYCLACHAENA (Eresenius) Gray. Heads in panicled spikes, scarcely 

 bracteate ; corolla of the 6 fertile flowers a mere rudiment or none. 



4. I. xanthifblia Nutt. Annual, tall, roughish ; leaves nearly all opposite, 

 hoary with minute down, ovate, rhombic, or the lowest heart-shaped, doubly or 

 inoisely toothed, or obscurely lobed ; heads small, crowded, in axillary and 

 terminal panicles. — Ont. and Mich, to Assina., Kan., westw. and soathwestw. ; 

 locally established eastw. 



40. AMBR6SIA [Tourn.] L. Ragweed 



Fertile heads 1-3 together, sessile in -axils of leaves or bracts, at the base of 

 racemes or spikes of sterile heads. Sterile involucres flatfish or top-shaped, of 

 7-12 united bracts, containing 5-20 staminate flowers, with or without slender 

 chaff intermixed. Anthers almost separate Fertile involucre (fruit) ellipsoid, 

 obovoid, or top-shaped, closed, pointed, resembling an achene and inclosing a 

 single flower; elongated style-branches protruding. Achenes ovoid.- — Coarse 

 homely weeds with opposite or alternate lobed or dissected leaves, and incon- 

 spicuous greenish flowers, in late summer and autumn ; ours annuals, except 

 the last. (The Greek and later Latin name of several plants, as well as of the 

 food of the gods.) 



6 1. Sterile heads sessiJe in a dense spike, the top-shaped involucre extended on 

 ' one side into a large lanceolate hooded bristly-hairy tooth or appendage; 

 fertile involucre ellipsoid or ovoid and i-angled. 

 ]. A. bidentata Miohx. Hairy, 3-9 dm. high, very leafy; leaves alternate, 



lanceolate, partly clasping, nearly entire, except a short lobe or tooth on each 



side near the base; fruit with 4 stout spines and a central beat. — Praiiies of 



111. to Kan., and southw. 



