About Galeopsis tetrahit L.
Common hemp-nettle (Galeopsis tetrahit L.) is an erect annual plant that reaches a height of 20 to 70 cm (8 to 28 in). Its stem is squarish, hairy, occasionally branched, and bears glandular hairs on the upper sections of the plant. The stem's nodes are swollen and widely spaced. The pale green, stalked leaves grow in opposite pairs; leaf blades are hairy, ovate with a long tapered tip, and have regular large teeth along the margin. The inflorescence is a terminal spike made up of whorls of pinkish flowers that have dark markings on the lower lip. Each flower's calyx has five sharp-pointed lobes, and the corolla forms a fused two-lipped tube 15 to 20 mm (0.6 to 0.8 in) long. The upper lip of each flower is convex and covered in dense glandular hairs, while the lower lip is three-lobed; the central lobe is the largest, squarish, and has a flat or rounded edge. There are four stamens total, two long and two short. The gynoecium has two fused carpels, and the mature fruit is a four-chambered schizocarp. This plant has a slightly unpleasant odor.
Common hemp-nettle is native to Europe and northwestern Asia. Its typical habitats include rough ground, arable land, logging clearances, and waste places. It spreads easily because its sharp calyces stick to clothing and animal fur.
