fireweed, any of several plants that spring up in fire-swept regions, especially the great willow herb Epilobium, which is classified in the family Onagraceae (evening primrose family).

Perennial wildflower (Epilobium angustifolium) of the evening-primrose family. Its spikes of whitish to magenta flowers, which grow up to 5 ft (1.5 m) high, can be a spectacular sight on prairies of the temperate zone. Its seeds can lie dormant for many years, awaiting the warmth necessary for germination. Fireweed is one of the first plants to appear after a forest or brush fire; it also rapidly covers scrub or woodland areas that have been cleared by machine. It has limited use in wild gardens, where it must be carefully checked and confined.

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