- Name also: Garden Loosestrife, Yellow Garden Loosestrife
- Family: Primrose Family – Primulaceae
- Growing form: Perennial herb. Rhizomatous, with runners.
- Height: 20–160 cm (8–64 in.). Stem slightly ascending from base, unbranched, upper part fine-haired, lime green–reddish brown, often spotted.
- Flower: Corolla regular (actinomorphic), wheel-shaped, yellow, 8–16 mm (0.32–0.64 in.) wide, fused, short-tubed, 5-lobed, lobes with roundish tips, edge glabrous. Calyx lobes narrow, with reddish brown margins. Stamens 5. Pistil a fused carpel. Inflorescence a lax, terminal, compound raceme, flowers abundant in groups.
- Leaves: Whorled or opposite, almost stalkless. Leaf blade ovate–lanceolate, sharp-tipped, with entire margins, dark-spotted, underside fine-haired.
- Fruit: Spherical, 5-valved, longer than calyx, approx. 4 mm (0.16 in.) long capsule.
- Habitat: Shores, damp meadows, ditches, stream banks, damp broad-leaved forests, roadside embankments.
- Flowering time: June–August.
Yellow loosestrife’s early life is special: the shoot only grows as big as a hand-span when it sends out a runner, which then takes root and grows into a full-size plant. Loosestrifes often form broad stands with the help of this rambling rootstock. Apart from efficient vegetative propagation, yellow loosestrife often flowers abundantly at the end of the summer. The flowers have no nectar, but abundant amounts of pollen attract flies and bees as pollinators. The shoot sticks up all through the winter and the wind rattles the seeds in their round capsules.
Yellow loosestrife’s original habitats are different kinds of rich wetlands, where it often grows close to the water line. The plant’s yellow flowers can also be admired in towns, on damp meadows, ditch banks and park margins. Yellow loosestrife would be a suitable and undoubtedly popular ornamental but its place has already been taken by dotted loosestrife (L. punctata), which looks similar and has a more abundant inflorescence.
Yellow loosestrife is also a versatile, useful plant. No comprehensive study has yet been made of its medicinal properties, but traditionally it has been used to treat bleeding and wounds. The plant has been put to other uses too: its roots yield a brown dye and its leaves a yellow one, and a strong infusion of the flowers can lighten the colour of one’s hair.