201b. Heads 12-50 mm. wide --203. 202a. Flower-clusters flat-topped =Yarrow, Achillea millefolium.= 202b. Flower-clusters very convex =Yarrow, Achillea lanulosa.= 203a. Principal leaves pinnatifid --213a. 203b. Principal leaves 1-3 times pinnately parted or dissected --204. 204a. Leaf-segments very narrowly linear; leaves 2-3-pinnate --205. 204b. Leaf-segments linear or lanceolate; heads 2.5-5 cm. wide =Camomile, Anthemis arvensis.= 204c. Leaf-segments ovate to ovate-oblong; heads 1-2 cm. wide =Feverfew, Chrysanthemum parthenium.= 205a. Foliage strongly scented =Dog Fennel, Anthemis cotula.= 205b. Foliage not ill-scented =Wild Camomile, Matricaria inodora.= 206a. Heads 3-6 mm. broad, including the rays (summer and autumn) --207. 206b. Heads 7 mm. broad or larger, including the rays --209. 207a. Rays purple (1-4 dm. high) =Horse Weed, Erigeron divaricatus.= 207b. Rays white --208. 208a. Leaves obovate to oblong (3-10 dm. high) --135a. 208b. Leaves linear or narrowly lanceolate (2-25 dm. high) =Horse Weed, Erigeron canadensis.= 209a. Pappus none, or minute and not of hairs (summer and autumn) --210. 209b. Pappus of hairs --214. 210a. Disk-flowers purple or brown (4-12 dm. high; rays pink) (Purple Coneflower) --211. 210b. Disk-flowers yellow or nearly white --212. 211a. Leaves ovate or ovate-lanceolate, most of them serrate =Purple Coneflower, Brauneria purpurea.= 211b. Leaves narrowly lanceolate, gradually narrowed at the base, entire =Purple Coneflower, Brauneria pallida.= 212a. Rays broadly obovate; heads 1-2 cm. wide (3-6 dm. high) =Sneezewort, Achillea ptarmica.= 212b. Rays oblong or narrowly elliptical --213. 213a. Leaves serrate (3-10 dm. high) =Ox-eye Daisy, Chrysanthemum leucanthemum var. pinnatifidum.= 213b. Leaves entire (8-25 dm. high) =Boltonia, Boltonia asteroides.= 214a. Involucral bracts all the same length or nearly so and narrow, or with a few short outer ones; plants blooming in spring and summer, or a few plants persisting in bloom until autumn (Fleabane) --215. 214b. Involucral bracts unequal, the outer successively shorter (or rarely nearly equal), loosely or closely overlapping; plants 3-15 dm. high, blooming in late summer and autumn (Aster) --221. 215a. Rays short and inconspicuous, barely longer than the pappus (1-5 dm. high; summer) =Fleabane, Erigeron acris var. asteroides.= 215b. Rays conspicuous, spreading, 3 mm. long or more --216.