This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual. Propagates by seeds.
Time of bloom: June to November. Seed-time: July to December. Range: Massachusetts to Oregon, southward to Georgia and Mexico. Habitat: Gardens, roadsides, and waste places.
An immigrant from South America which has also crossed the ocean and been reported as troublesome in southern Europe. Stem one to two feet tall, pale green, slender, many-branched and spreading, sparsely clothed with ap-pressed hairs. Leaves opposite, ovate, thin, three-nerved, scallop-toothed, acute at apex, the lower ones narrowing to slender petioles, the upper ones sessile or nearly so. Heads, hardly a quarter-inch broad, solitary on short, slender peduncles, terminal and in the upper axils; rays white, very short, three-toothed, pistillate, fertile; disk-florets yellow, perfect, and fertile; bracts of the involucre smooth, the outer row shorter. Achenes very small, dark, four-sided, wedge-shaped, finely hairy. (Fig. 333.)
Fig. 333. - Galinsoga (Ga-linsoga parviflora). X 1/4.
Prevent seed production by pulling or hoe-cutting when in first flower. In cultivated ground the weed is destroyed by the tillage of the crop.