Rattlesnake root is like a slender version of rosebay willow-herb (US “fireweed”; Epilobium angustifolium): the stem is slim and drooping and from the tips of the even slimmer side-stems hang clusters of small red-violet composite flowers. The generic name Prenanthes means “flowering face-down”. Each seed has a tuft of hairs which helps with wind dispersal to new areas.
How easily they spread can be seen in Mustila’s Alppiruusulaakso (Rhododendron Valley), where this shade-loving forest perennial has gradually developed into a troublesome weed. Unlike rosebay willow-herb, rattlesnake root thrives in shade so long as the soil is rich. Cutting immediately after flowering is one of the routine jobs aimed at preventing further spread of the seeds. However, rattlesnake root also spreads underground. Weeding simply encourages the roots to spread faster, so the only way to remove it from unwanted sites is by using weed-killer.