226b. Leaves serrate --228.
227a. Leaves glabrous above =Aster, Aster shortii.=
227b. Leaves rough above =Aster, Aster azureus.=
228a. Involucre 4-6 mm. long --229.
228b. Involucre 6-10 mm. long --230.
229a. Leaves rough; petioles mostly winged =Aster, Aster lowriea.n.u.s.=
229b. Leaves smooth; petioles slender, not winged =Aster, Aster cordifolius.=
230a. Heads few, seldom more than 10, in a loose spreading cl.u.s.ter =Aster, Aster lindleya.n.u.s.=
230b. Heads numerous, in a rather elongate crowded cl.u.s.ter =Aster, Aster sagittifolius.=
231a. Stem hirsute or rough-p.u.b.escent --232.
231b. Stem smooth, or essentially so --236.
232a. Leaves conspicuously serrate =Aster, Aster puniceus.=
232b. Leaves entire or nearly so --233.
233a. Leaves narrowed toward the base and barely clasping, linear or oblong-linear --234.
233b. Leaves ovate-oblong or lanceolate, with a broad conspicuously clasping base --235.
234a. Involucre p.u.b.escent but not glandular =Aster, Aster amethystinus.=
234b. Involucre glandular =Aster, Aster oblongifolius.=
235a. Involucre very glandular and viscid; rays very numerous, violet-purple; leaves lanceolate =Aster, Aster novae-angliae.=
235b. Involucre slightly glandular or not at all; rays 20-30, generally blue-purple; leaves ovate-oblong =Aster, Aster patens.=
236a. Leaves of a linear type --237.
236b. Leaves broader than linear, at least 1 cm. wide --238.
237a. Bracts narrow, approximately equal in length --253a.
237b. Bracts of several lengths, the outer successively shorter --256a.
238a. Leaves smooth above =Aster, Aster laevis.=
238b. Leaves rough above --239.
239a. Leaves contracted below the middle and then abruptly dilated to the clasping base =Aster, Aster prenanthoides.=
239b. Leaves gradually narrowed toward the base =Aster, Aster puniceus.=
240a. Rays conspicuous --241.
240b. Rays minute or wanting =Aster, Aster angustus.=
241a. Stems and leaves gray with a silky p.u.b.escence =Aster, Aster sericeus.=
241b. Stem and leaves green, not silky --242.
242a. Bracts glandular-viscid; rays violet =Aster, Aster oblongifolius.=
242b. Bracts bristly-ciliate --243.
242c. Bracts smooth or p.u.b.escent, not glandular or bristly-ciliate --244.
243a. Leaves crowded, rigid; rays white =Aster, Aster multiflorus.=
243b. Leaves not crowded and rigid; rays blue --234a.
244a. Bracts narrowed at the tip into thickened firm green awl-shape points --245.
244b. Bracts acute or obtuse at the flattened tip --247.
245a. Involucre 4-5 mm. long --246.
245b. Involucre 7-8 mm. high =Aster, Aster polyphyllus.=
246a. Stem smooth =Aster, Aster ericoides.=
246b. Stem hairy; leaves linear =Aster, Aster ericoides var. villosus.=
246c. Stem densely white-woolly =Aster, Aster ericoides var. platyphyllus.=
247a. Leaves at most 4.5 cm. long --248.
247b. Leaves larger, at least the princ.i.p.al ones --249.
248a. Stems in cl.u.s.ters; leaves rigid, linear, with 1 vein; flowers blue =Aster, Aster linariifolius.=
248b. Stem solitary; leaves not rigid; flowers rose-pink =Aster, Aster nemoralis.=
249a. Heads solitary at the end of minutely leafy branchlets; leaves linear =Aster, Aster dumosus.=
249b. Heads in flat-topped cl.u.s.ters; leaves lanceolate or broader --250.
249c. Heads in more or less one-sided racemes --251.