- Name also: Henbit Deadnettle, Greater Henbit
- Family: Mint Family – Lamiaceae (Labiatae)
- Growing form: Annual herb.
- Height: 10–30 cm (4–12 in.). Stem ascending–erect, base branching, branches ascending, 4-edged, upper part soft-haired, internodes often long.
- Flower: Corolla irregular (zygomorphic), purplish red, 15–20 mm (0.6–0.8 in.) long, fused, bilabiate, long-tubed. Upper lip convex, 3–5 mm (0.12–0.2 in.) long; lower lip 1.5–2.5 mm (0.06–1 in.) long, central lobe obcordate, lateral lobes small. Calyx almost regular (actinomorphic), 5-lobed, 5-veined, lobes at most same length as calyx tube, closed after flowering. Stamens 4, of which 2 short and 2 long. Gynoecium composed of 2 fused carpels. Inflorescence terminal, spike-like, comprised of dense, axillary whorls. Often also with small, unopened (cleistogamous) flowers.
- Leaves: Opposite, lower leaves stalked, upper stalkless, amplexicaul, often with fused base. Blade kidney-shaped, net-veined, hairy, margins with several large rounded teeth. Inflorescence’s subtending bracts like stem leaves.
- Fruit: 4-parted schizocarp. Mericarps bristly, brown.
- Habitat: Gardens, fields, soil heaps, waste ground.
- Flowering time: May–September.
Henbit dead-nettle is probably native to the Mediterranean area, but it has spread as a weed around the world. It has adapted to live in cultivated land, gardens and similar places where people do not want them. Henbit dead-nettle grows quickly and spreads efficiently. Apart from its normal flowers it also has closed (cleistogamous) flowers. They are self-pollinating because the corollas do not open to pollinators. They are often produced especially at cool times of year when there are no pollinators around. Thus the plant saves its resources and ensures pollination – self-pollination is actually common among open flowers too. Most Finnish plants time their flowering to coincide with a certain season, but henbit dead-nettle is very flexible: it can flower in the middle of summer or just as easily at the end. In favourable conditions its flowering time continues all through the year. Its seeds have an oily appendage (elaiosome) which attracts ants on food-finding trips, which then spread the seeds to new habitats.
It can be difficult to differentiate between different species of red-flowered dead-nettle. Henbit dead-nettle’s uppermost stem leaves are amplexicaul: their cordate base surrounds the stem like a collar. There is also an important identification marker in the calyx, whose lobes close up after flowering. This is unlike its relatives.