This section is from the book "Harper's Guide To Wild Flowers", by Caroline A. Creevey. Also available from Amazon: Harper's Guide To Wild Flowers.
Family, Mint. Color, purple. Calyx, with 5 equal teeth. Corolla, with upper lip arched, curved, not lobed; lower, 3-cleft, the middle inversely heart-shape. Throat, with 2 teeth in the folds. Flowers, in whorls in axils of the upper leaves. Stem, very hairy, swollen below its joints. Leaves, ovate, coarsely serrate. August and September.
Low, branching plant, common in waste places and dry fields.
 
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