This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Annual. Propagates by seeds.
Time of bloom: July to October.
Seed-time: August to November.
Range: Nova Scotia to British Columbia, southward to the Carolinas, Missouri, and California; also in Europe and Asia. Habitat: Marshy meadows, swamps, and along streams.
This species, usually in company with the similar, but larger, Brook Sunflower (Bidens laevis, B.S.P.), often covers acres of lowlands with yellow bloom, to be succeeded by the clutching brown fruits. It is small, six to thirty inches high, pale green, smooth, or sometimes slightly rough-hairy, rather stout, with short branches. Leaves opposite, narrowly lance-shaped, sessile, often joined at base, edged with coarse, distant, and unequal teeth. Heads numerous, large, broader than their height, the peduncles short and at first erect but drooping after fertilization; rays often lacking, but, when present, bright yellow, exceeding the length of the disk by about one-half; disk-florets orange-yellow, five-lobed; outer bracts of the involucre longer than the head, usually bristle-fringed and spreading; the inner row short, ovate, pointed, with yellowish, scarious margins. Achenes wedge-shaped, dull brown, four-angled, four-awned, angles and awns barbed downward, causing these fruits to be even more readily attached to clothing and the coats of animals than those of the preceding species. (Fig. 330.)
' The same measures for suppression are necessary as for the Swamp Beggar-tick.
Fig. 330. - Nodding Bur Marigold (Bidens cernua).