Epilobium hirsutum is a semi-aquatic perennial herbaceous plant. The plant is erect, branching, covered with soft hairs and grows up to 6 ft. (1.8 m) tall. E. hirsutum is native to Africa, temperate Asia and Europe.
Foliage
E. hirsutum leaves are opposite, sessile and clasp the stem. Leaf blades are lanceolate-elliptic to narrowly obovate or elliptic 1.6-4.7 in. (4-12 cm) long and 0.12-1.6 in. (0.3-4 cm) wide. Foliage is villous both above and below with a serrulate margin. Leaf tip is acute to acuminate.
Flowers
Solitary flowers are held on stems arising from the upper leaf axils. Stems can be floating or lying on the ground. The flowers are showy with bright pink to dark purple notched petals with white centers.
Fruit
E. hirsutum reproduces by seeds, rhizomes and stolons. Fruits are narrow, pubescent, dehiscent seed pods from 1-3.5 in. (2.5-9 cm) long that contain numerous seeds. Seeds have long white hairs that aid in dispersal by wind.
Ecological Threat
E. hirsutum is an extremely widespread and variable species that spreads aggressively by vegetative growth in sunny open wetland habitats, although it can also invade uplands. It can form monocultures in natural wetlands, crowding out native species.