The rosebay willowherb thrives on railway embankments, and was spread throughout Britain by the building of the railways. Introduced to gardens for its brilliant magenta flowers, a single rosebay willowherb can produce 80,000 seeds a year, each with its own silk parachute. The rush of air from the trains wafted these seeds far and wide. The plant also earned the name fireweed because it thrived on ground that was newly burned from the trains' sparks. Rosebay thus spread all across the country.