- Family: Mint Family – Lamiaceae (Labiatae)
- Growing form: Annual herb.
- Height: 20–50(–70) cm (8–20(–25) in.). Stem only slightly swollen at joints, often reddish, 4-edged, edges rough-haired, sometimes also with glandular hairs, glandular hairs’ head pale.
- Flower: Corolla irregular (zygomorphic), usually pink or yellowish white, 12–15 mm (0.48–0.6 in.) long, fused, bilabiate, long-tubed, hairy. Upper lip convex; lower lip 3-lobed, central lobe with dark markings, with yellow base, with narrowly pale margins, clearly longer than broad, often convex, with notched tips, margins revolute, base with 2 glands. Calyx campanulate (bell-shaped), 5-lobed, lobes rigid, sharp-pointed. Stamens 4, of which 2 short and 2 long. Gynoecium composed of 2 fused carpels. Inflorescence spike-like, lower part with large spaces, upper part dense, cluster formed of dense axillary whorls, terminating stem and branches.
- Leaves: Opposite, stalked. Blade ovate–broadly elliptic, top often long-tapered, feather-veined, densely haired flush with surface, underside often also with glandular hairs, margin low-toothed. Inflorescence’s subtending bracts like stem leaves.
- Fruit: 4-parted schizocarp. Mericarps elliptic, flattish, almost glossy, brown.
- Habitat: Arable land, waste ground, gardens, soil heaps, roadsides, logging sites, sea shores, rocky outcrops.
- Flowering time: July–September.
Bifid hemp-nettle grows in many places as a weed in cultural environments, but also far from habitation on sea shores and even the outer archipelago. It has grown in Finland as a native plant on piles of debris that the waves deposit on shores and also in waterside woods and rocky outcrops. The flowers are a pale creamy colour. Additionally, there is another established population that arrived in ancient times with people, and this is mainly red-flowered and grows in fields and waste ground. It is difficult to draw a line between these populations because they are often mixed up and both often grow nowadays in the same habitat.
Bifid hemp-nettle is a common field weed. It sheds its seeds before they are threshed, so a single plant can ripen even hundreds. Part of them fall to the root of the mother plant and part spread to new growing places, usually with animals either by attaching to their fur or passing through their digestive tract. The seeds remain viable for even decades. Often bifid hemp-nettle grows in logging clearings as a memory of a time when the forest was used for pasture, slash-and-burn agriculture, and for making tar.
Bifid hemp-nettle is the only native representative of its genus in Finland. It can be confused with similar-looking common hemp-nettle (G. tetrahit), which it was formerly seen as a variation or mutation of. The best distinguishing features are found in the small flowers: the central lobe on common hemp-nettle’s lower lip is quite square and it lacks a notch.