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..
Aster sagittifolius Willd. Sp. Pl. 3: 2035. 1804.
Stem stout, or slender, strict, glabrous, or sparingly pubescent above, 2°-5° high, paniculately branched at the inflorescence, the branches ascending. Leaves thin, slightly roughened, or glabrous above, glabrate or pubescent beneath, the lower and basal ones cordate or sagittate, ovate-lanceolate, sharply serrate, acuminate, 3'-6' long, with slender naked or narrowly margined petioles; upper leaves lanceolate, sessile, or on short and usually margined petioles, serrate or entire, those of the branches very small; heads 2 1/2"-4" high, 8"-10" broad, numerous, crowded, racemose; involucre turbinate, its bracts linear-subulate, glabrous or nearly so, their tips green and slightly spreading; rays 10-15, light blue or purplish, 3"-4" long; pappus whitish.
In dry soil, New Brunswick to Ontario, North Dakota, New Jersey, Georgia and Missouri. Aug.-Oct.
Aster Saundersii Burgess, of the Dakotas and Iowa, differs by a corymbose inflorescence.
Aster undulatus L. Sp. Pl. 875. 1753.
Stem stiff, very rough and pubescent, divaricately branched above, 1°-3 1/2° high. Leaves usually thick, rough on both sides, pubescent beneath, dentate, undulate or entire, acute or acuminate, the lowest and basal ones ovate, cordate, 2'-6' long, with naked or margined petioles; middle ones ovate, lanceolate or oblong, with margined petioles dilated and clasping at the base, the upper sessile or clasping, those of the branches small and subulate; heads numerous, racemose and often secund on the spreading branches, about 4" high, 8"-10" broad; involucre broadly turbinate, its bracts linear-oblong, pubescent, acute or acut-ish, their green tips appressed; rays 8-15, pale blue to violet, 3"-5" long; pappus whitish.
In dry soil, New Brunswick and Ontario to Minnesota, Florida, Alabama, Louisiana and Arkansas. Various-leaved aster. Races differ in leaf-form and inflorescence. Sept.-Oct.
Stem slender, rough, 1°-3° high, divergently branched. Leaves ovate-oblong to oblong-lanceolate, rough or pubescent, thick and somewhat rigid, strongly cordate or auriculate-clasping at the broad base, entire, acute, or the lowest obtuse, 1'-3' long, those of the branches much smaller and bract-like, the margins rough-ciliate; heads 1' broad or more, solitary at the ends of the branches; involucre broadly turbinate, its bracts linear-oblong, finely pubescent or scabrous and somewhat glandular, imbricated in several series, their green acute tips spreading; rays 20-30, purplish-blue, or deep violet, 4"-6" long; pappus tawny; achenes pubescent.
In dry, open places, Maine to northern New York, Minnesota, Florida, Louisiana and Texas. Reported from Canada. Races differ in leaf-form and pubescence. Aug. - Oct.