Epilobium is a genus of flowering plants in the evening primrose family and contains about 197 species. Willowherbs are mostly herbaceous plants, either annual or perennial and a few are subshrubs. Willowherbs are typically very quick to carpet large swathes of the ground and may become the dominant species of local ecosystems.

The hairy Willowherb or Codling-and-Cream is the one found most often in the eastern US and grows to 6 feet tall. It has hairy leaves and stalks and notched flower petals. Rock fringe is a prostrate form from the western United States. Fireweed can show up after a fire. Annual varieties are more common in cool regions but occur occasionally as a cool-season weed in warmer areas.

The plants are sometimes cultivated but must be carefully confined. Soil preference depends on the species as some invade wet areas and some prefer dry sites.