GENUS 87.] THISTLE FAMILY. 



2. Tanacetum Huronense Nutt. : ,- 



Lake Huron Tansy. (Fig. 3997-) H 



Tanacetum Huronense Nutt. Gen. 2: 141. 1818. 



Villous-pubescent throughout, at least when 

 youug, less so when mature, i-2 high.' Leaves 

 2-pinnately divided, the lobes dentate or incised, 

 acute, the lower segments commonly smaller 

 than the others; heads 1-8, 6 // -8 // broad, on very 

 stout pubescent peduncles; involucre depressed- 

 hemispheric; marginal flowers with 3-5-lobed 

 limbs, often expanded into short rays; pappus 

 a short crown. 



In moist soil, especially along streams or lakes, 

 New Brunswick to Hudson Bay, Maine, Lake 

 Superior, Alaska and Oregon. Juty-Sept. 



88. ARTEMISIA L, Sp. PI. 845. 1753. 



Odorous herbs or shrubs, often canescent or tomentose, with alternate leaves, and small 

 pendulous or erect, discoid racemose spicate glomerate or paniculate heads, of greenish or 

 yellowish flowers. Involucre ovoid, oblong, or broadly hemispheric, its bracts imbricated in 

 few series, the outer gradually shorter. Receptacle flat, convex or hemispheric, naked or 

 pubescent, not chaffy. Central flowers perfect, sometimes sterile, with abortive ovaries and 

 undivided styles, sometimes perfect and fertile, with truncate style-branches; marginal flow- 

 ers usually pistillate and fertile, their corollas 2-3-toothed; or flowers all perfect and fertile 

 in some species. Authers obtuse and entire at the base, often tipped with subulate appen- 

 dages. Achenes obovoid or oblong, 2-ribbed or striate, rounded at the summit, usually 

 bearing a large epigynous disk. Pappus none. [Named for Artemisia, wife of Mausolus.] 



About 200 species, natives of the northern hemisphere and southern South America. Besides 

 the following, some 25 others occur in the western parts of North America. 



X Marginal flowers pistillate ; central flowers perfect, sterile. 

 a. Biennial or perennial herbs. 



Leaves pinnate^- dissected into narrowly linear lobes. 



Heads very numerous, 1" broad; leaves mostly glabrous. 

 Heads 2" broad, in narrow panicles; leaves silky-pubescent. 



Heads few; involucre brown, mostly pubescent. 2. 



Heads numerous; involucre green, mostly glabrous. 3. 



Leaves linear, the lower sometimes 3-cleft or pinnately divided. 



Leaves glabrous. 4- 



Leaves finely and densely pubescent. 5' 



b. Shrubby, silvery-canescent; heads small and numerous. 6. A. filifolia 

 -;:- X Marginal flowers pistillate ; central flowers perfect, fertile. 

 a. Receptacle villous-pubescent. 

 Leaf-segments linear-filiform, short. 

 Leaf-segments oblong, or linear-oblong; introduced. 



b. Receptacle glabrous, or sparingly pubescent 

 Leaves dissected, glabrous or pubescent, green, not tomentose. 



Heads about 2" broad, numerous in panicled racemes; perennial. 

 Heads about 1" broad, paniculate or spicate; annuals. 



Leaves finely 2-3-pinnately divided; heads paniculate. 10. A. annua. 



Leaves pinnately divided; segments pinnatifid; heads in leafy spikes. 11. A. biennis 

 Leaves densely white-canescent or tomentose, at least beneath. 

 Leaves pinnatifid or dissected. 



Heads 3" -4" broad, racemose-glomerate; sea-beach plant. 

 Heads i"-2" broad, spicate-paniculate or racemose. 



Leaves deeply pinnatifid, the segments mostly incised. 

 Leaves finely dissected into short linear lobes. 

 Leaves pinnately parted into 5-7 narrow entire segments. 

 Leaves lanceolate or linear, serrate or entire, not pinnatifid. 

 Leaves lanceolate, sharply serrate, glabrous above. 

 Leaves linear, oblong, or lanceolate, entire or lobed. 

 Leaves elongated, at length glabrous above. 

 Leaves shorter, oblong or lanceolate, tomentose both sides. 

 Leaves cuneate, %' long, 3- toothed at the apex. 



X- X- * Flowers all perfect and fertile ; far western species. 

 Leaves" cuneate, 3-toothed or 3-lobed. 20. 



Leaves linear, entire. 21. 



1. A. caudata. 



A. boreal is. 

 A. Canadensis. 



A. dracunctiloides. 

 A. glauca. 



7. A. frigida. 



8. A. Absinthium. 



9. A. Abrotanum. 



12. A. Stelleriana. 



13. A. vulgaris. 



14. A. Potitica. 



15. A. Kansana. 



16. A. serrata. 



18. 

 19- 



A. longifolia. 

 A. gnaphalodes. 

 A. Bigelozii. 



A. tridentata. 

 A. cana. 



