This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual and winter annual. Propagates by seeds.
Time of bloom: June to September.
Seed-time: July to October.
Range: Nova Scotia to Manitoba, southward to Florida and
Missouri. Habitat: Cultivated ground; clover and alfalfa fields, meadows, and waste places.
First cultivated in gardens because of its fragrance and beauty, but now a widespread pest. Stem one to three feet tall, erect, rather stout, branching, covered with glandular, viscid hairs. Basal and lower leaves three to five inches long, spatulate, narrowing to margined petioles; upper leaves sessile, often uniting around the stem; ovate to lance-shaped, acute. Flowers in spreading cymes, few but large, often more than an inch across, very fragrant, creamy white, with five deeply cleft petals opening at twilight to close again at sunrise; stamens ten; styles three; calyx-tube more than a half-inch long, becoming much inflated and showing beautiful ten-lined markings in two shades of green. Capsule ovoid, six-toothed at the opening, and containing many grayish brown seeds roughened with rows of fine tubercles; these seeds are very difficult of removal from those of clover and alfalfa. (Fig. 99.)
Sow clean seed. In fields to be harvested for seed the weed should be hand-pulled at the opening of its earliest flowers. Where practicable, cut young plants from their roots with spud or hoe, well below the crown. Rankly infested fields should be broken up and put under cultivation for a season.