Lythrum salicaria vars. The original spelling Lythrum hyssopifolia L. is sometimes used. A mature plant can develop into a large clump up to 1.5 m in diameter. Above ground foliage usually dies during the cool season, and new shoots sprout from a broad woody crown in spring. Originally cultivated as an ornamental and medicinal herb, purple loosestrife has escaped cultivation and become a noxious weed of wetlands in many regions throughout temperate North America.
Plants often form dense colonies that displace native vegetation and wildlife.
In the Northeastern U.S., monotypic stands have perpetuated themselves for at least 20 years. Introduced from Eurasia. They are established in some areas, but do not exist in California at publication time. Prostrate to erect summer annual or biennial with small pale pink to lavender flowers , to 0.6 m tall. Hyssop loosestrife is a common weed of seasonal wetlands and agronomic crops, especially rice fields.