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 August. Seed-time: August to October. Range: Newfoundland to British Columbia and Alaska, southward to North Carolina and Michigan. Habitat: Fields, pastures, roadsides, and waste places.
Grazing cattle shun this weed, and gloves are needed in handling it when full-grown. Stem one to three feet tall, stout, four-sided, swollen below the joints, much branched and spreading, bristling with prickly hairs. The opposite leaves are ovate, long-pointed, coarsely toothed, bristly-hairy on both sides, and with bristly petioles. Flowers in a dense, short, leafy-bracted terminal spike and in axillary clusters; corolla nearly an inch long, pink or pale purple, with a stiff, concave entire upper lip, longer than the lower one, which has three lobes; the tube is about twice the length of the bristly calyx, which has five long, nearly equal awl-like points. Seeds four small, flattened, ovoid nutlets. (Fig. 245.)
Prevent reproduction by close cutting while young. If nearing maturity when cut the weed should be removed from the ground, as the large, swollen stems contain enough nutriment to ripen the seed.