This plant grows up to about 9 feet tall and is a member of the Asteraceae. The stem is strongly grooved and the alternate leaves have irregular lobes with uneven edges. The white flowers are inconspicuous as they have no ray flowers (the outer, petal-like flower found in many members of the Aster Family to attract insect pollinators). The central disk flower has a sheath of bracts (reduced leaves at the base of a flower stalk) which is enlarged at the base. Each seed developed within the disk flower has a mass of fine hairs, for wind dispersal, which can be seen sticking out from the sheath of bracts.

Pilewort or fireweed is found in old fields and disturbed areas, often where the soil is moist. The leaves are eaten in some places or used to make tea. Leaves have also been used for medicinal purposes. It has quite a strong smell.

A completely unrelated plant (Epilobium angustifolium) with red flowers is also known as fireweed.