This large shrub is so called because it is visited by large numbers of butterflies and moths, as it is an extremely good source of nectar (2). Indeed, the spread of this plant may have been the single factor responsible for the maintenance of many urban butterfly populations (4). The plants has dark green lance-shaped leaves, which are white on the undersides. The purple flowers are densely arranged in flower spikes (2).
This deciduous shrub has spread so well throughout Britain because the light seeds are winged and have extremely good powers of dispersal. The railways have acted as corridors for dispersal, from which the species has spread outwards (4). In more southerly areas it often forms very dense shrubberies (4).
Although still popular in gardens, this species has escaped from cultivation and is now a common feature of waste ground, roadsides and railways, quarries and a range of urban habitats. It shows a preference for dry and disturbed sites (3).
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