White butterbur
White Butterbur (Petasites albus) flowers early in the year, generally between February and May. The flowers are white and spiked, and dominate damp areas beside rivers. When flowering, the leaves are small; however, they can reach a width of up to 30cm after the plant has finished flowering. Visually, the leaves are similar to those of a rhubarb plant, with a slightly more heart-like shape. The leaves grow close to the ground, which created a dense carpet that covers the ground.
Butterbur has a rhizome root, so spreads readily in the damp ground along rivers and road verges. It can regenerate from fragments of rhizome, which can be carried along river corridors by the water. It has invaded many areas of disturbed flood-prone ground.
Butterbur roots spread easily in damp ground, making riverbeds a near-perfect habitat. The roots can regenerate from fragments, which can be carried along waterways by the current; this is a leading cause of the spread of this plant.
White Butterbur is very similar to Common Butterbur (Petasites hybridus) which is a native plant. The main difference between the two species is the flowers; White Butterbur has five narrow white petals, with long pale-green sepals. Common Butterbur has thicker petals, with much shorter sepals. The leaves of both species are difficult to differentiate, as both species have long leaves with a white felted underside.
In the UK, White Butterbur is more concentrated in North Eastern Scotland. It was first introduced from Asia and, like many invasive plants, was planted as an aesthetic garden ornament before they spread into the natural environment.
More information on White Butterbur can be found here.
