This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol3", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
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 style, sometimes perfect and fertile, with truncate style-branches; marginal flowers usually pistillate and fertile, their corollas 2-3-toothed, or flowers all perfect and fertile in some species. Anthers obtuse and entire at the base, often tipped with subulate appendages. 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 225 species, natives of the northern hemisphere and southern South America. Besides the following, some 40 others occur in the western parts of North America. Type species: Artemisia vulgaris L.
* Marginal flowers pistillate; central flowers perfect, sterile.
a. Biennial or perennial herbs.
Leaves pinnately dissected into narrowly linear lobes.
Heads very numerous, 1" broad; leaves mostly glabrous.
1. A. caudata.
Heads 2" broad, in narrow panicles; leaves silky-pubescent.
2. A. boreal is.
Heads few; involucre brown, mostly pubescent.
3. A. canadensis.
Heads numerous; involucre green, mostly glabrous. Leaves linear, the lower sometimes 3-cleft or pinnately divided. Leaves glabrous.
4. A. dracunculoides.
Leaves finely and densely pubescent.
5. A. glauca.
b. Shrubby, silvery-canescent; heads small and numerous.
6. A. filifolia.
** Marginal flowers pistillate; central flowers perfect, fertile. a. Receptacle villous-pubescent. Leaf-segments linear-filiform, short; native.
7. A. frigida.
Leaf-segments oblong, or linear-oblong; introduced.
8. A. Absinthium.
b. Receptacle glabrous, or sparingly pubescent. Leaves dissected, glabrous or pubescent, green, not tomentose.
Heads about 2" broad, numerous in panicled racemes: perennial.
9. A. Abrotanum.
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.
12. A. Stellariana.
Heads 1-2 broad, spicate-paniculate or racemose.
Leaves deeply pinnatifid, the segments mostly incised.
13. A. vulgaris.
Leaves finely dissected into short linear lobes.
14. A. Pontica.
Leaves pinnately parted into 5-7 narrow entire segments.
15. A. kansana.
Leaves lanceolate or linear, serrate or entire, not pinnatifid. Leaves lanceolate, sharply serrate, glabrous above.
16. A. serrata.
Leaves linear, oblong, lanceolate or obovate, entire or lobed. Leaves at length glabrous above.
Leaves linear, elongated, all entire.
17. A. longifolia.
Leaves various, at least the lower pinnately lobed or toothed. Involucre densely woolly; leaf-lobes broad.
18. A. ludoviciana.
Involucre loosely woolly; leaf-lobes linear.
19. A. mexicana.
Leaves shorter, oblong or lanceolate, tomentose both sides.
20. A. gnaphalodes.
Leaves cuneate, 1/2' long, 3-toothed at the apex.
21. A. Bigelovii.
*** Flowers all perfect and fertile; far western species. Leaves cuneate, 3-toothed or 3- lobed.
22. A. tridentata.
Leaves linear, entire.
23. A. cana.