This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Perennial. Propagates by seeds.
Time of bloom: May to August.
Seed-time: June to September.
Range: Manitoba to the Northwest Territory, southward to New
Mexico, Texas, and Louisiana. Habitat: Prairies; dry fields and meadows.
A native relative of the garden Four o'clock, and a very persistent weed, having a large, fleshy, deep-boring taproot which makes it a gross feeder and about as hard to dislodge as the Curled Dock. Stem one to three feet tall, angled, smooth or nearly so, branching by repeated forking. Leaves opposite, smooth, entire, two to four inches long, broadly ovate or heart-shaped, and all peti-oled except the uppermost pairs. Flowers in forking terminal clusters, the peduncles and pedicels all somewhat hairy; subtending each cluster of three to five flowers is a saucer-shaped or umbrellalike involucre, five-lobed, persistent, and enlarging as the flowers mature until it becomes nearly an inch broad, thin, and net-veined, acting as a parachute in the distribution of the seeds; each small blossom has a bell-shaped five-lobed, red perianth, with three to five stamens and one style, both exserted. Ovary one-celled, the fruit a small, hard, achene-like, narrowly obovoid, ribbed, and hairy nutlet, possessed of long vitality. (Fig. 82.)
Fig. 82. - Heart-leaved Umbrella-wort (Oxybaphus nycta-gineus). X 1/3.
Prevent seeding. Cultivation will cleanse infested fields of the perennial roots, but small areas newly contaminated should be hand-pulled when the ground is soft, or should be grubbed out, or cut close to the ground and the fleshy root-crowns treated with salt in order to prevent too swift a recovery.