148 SELECTED WESTERN FLORA 



1. A. ludovicldna, Nutt. Westekn Wormwood. 



Perennial, white-woolly throughout; leaves entire or the lower Variously 

 cut, lanceolate; heads sessile in slender panicles. Dry soil, Man.-Alta. 



2. A. biennis, Willd. 



Herbaceous, biennial, tall, 1-4 ft. high, erect, strict; leaves dark green, 

 once or twice pinnatifid into linear, sometimes toothed lobes; heads small, 

 crowded on axillary spikes collected in a long compound spike-like cluster ; 

 only slightly odorous when bruised. A common weed in cultivated ground. 



3. A. frigida, Willd. 



Low, tufted, perennial, woody at the base, densely silky-eanescent through- 

 out; leaves much cut into narrow lobes; heads small, racemed. Arid soil, 

 often covering the ground, Man.-AIta. 



4. A. glauca. Pall. 



Erect, 1-2 ft. high, woody at the base, silky-pubescent or glaucous; 

 leaves mostly entire, linear; heads numerous in a narrow panicle. Dry 

 prairie, Man.-Alta. ' 



5. A. absinthium, L. Common Wormwood. 



Stem 1-2 ft. high; leaves 2-3-pinnately divided; canescent throughout. 

 A s,trong-smelling herb common about towns, introduced. 



20. MATRICARIA. Wild Chamomile. 



Heads many-flowered, radiate; ray-flowers pistillate or wanting; 

 bracts of the involucre in a few rows; the outer row shorter; recep- 

 tacle conical, naked. Annual or biennial herbs with smooth, finely 

 divided leaves, and rather large heads with white rays or none, and 

 yellow disks. 



1. M. matricaridides, Porter. Pineapple-weed. 



Leaves 2 or 3-pinnately divided; rays wanting; bracts of the involucre 

 oblong, green, with white dry margins; disk conical, extending beyond the 

 involucre. (M. siutveolens, Buchanan.) A Pacific slope species introduced 

 east as far as Calgary. The bruised leaves have a pineapple odor. 



21. AMBROSIA. Ragweed. 



Usually monoecious, the fertile heads solitary or in small clusters 

 in the axils of the upper leaves, the sterile heads in spikes or racemes 

 terminating the stems; involucre of the sterile heads open, saucer- 

 shaped, containing 5-20 flowers; involucre of the fertile heads 

 closed, seed-like, one-flowered; pappus wanting. Coarse branching 

 herbs with lobed or cut leaves and small heads of greenish flowers. 



