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: June to September.
Seed-time: August to November.
Range: Nova Scotia to British Columbia, southward to Florida and New Mexico. Habitat: Moist meadows, fields, and waste places.
A conspicuous plant because of the deep violet color of its panicled spikes of flowers. Stem three to seven feet tall, erect, square, finely rough-hairy, coarsely grooved, and branching near the top. Leaves oblong lance-shaped, long-pointed, the lower ones often halberd-shaped at base, finely rough-hairy, double-toothed, darker above than below, with heavy veins and short, grooved petioles. Spikes numerous, very slender, the small, five-lobed, tubular flowers sometimes scattered along their length but usually grouped in a short circlet with a green stretch of buds above and another of growing and ripening fruits below. The small, brown nutlets usually drop from the stalk, calyx and all, without separating. They are a frequent impurity in clover and grass seeds.
Means of control the same as for White Vervain.
 
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