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..
Glabrous or minutely puberulent, light-green, mostly annual herbs, with opposite sessile entire or serrate leaves, and small 1-several-flowered, usually sessile, oblong and densely cymose-capitate heads of tubular, or both tubular and radiate yellow or yellowish flowers. Involucre of 2-5 narrow, nearly equal, appressed bracts, sometimes with 1 or 2 additional small exterior ones. Receptacle small, naked or setose. Ray-flower commonly only 1, pistillate, fertile, sometimes wanting. Disk-flowers 1-15, perfect, fertile, their corollas 5-toothed. Anthers entire at the base. Style-branches of the disk-flowers truncate. Achenes oblong or linear-oblong, 8-10-ribbed. Pappus none. [Latin, flavus, yellow, from its dyeing properties.]
About 7 species, natives of the warmer parts of America. In addition to the following, 3 others occur in the southern United States. Type species: Flaveria chilensis Gmelin.
Annual, glabrous, erect, 1°-2° high, little branched. Leaves linear or lanceolate, serrulate or entire, 3-nerved, acuminate or acute at the apex, sessile by a broad and somewhat clasping base, 1'- 2 1/2' long, 2"- 4" wide; heads about 3" high, closely sessile in terminal glomerules or these pedunculate from the upper axils; involucre of 3 oblong-lanceolate bracts, 2-5-flowered; ray equalling or longer than the breadth of the disk; achenes linear, glabrous, about 1 1/2 " long.