Also known as Black Knapweed, Common Knapweed grows wherever grass is not closely cropped. It is abundant beside lakes and streams in southern England, especially where grazing animals have been fenced off from the margins.
Like Common Knapweed, Greater Knapweed (Centaurea scabiosa) - pictured below - is also common throughout southern Britain, but grows in drier habitats such as calcareous meadows and downland.
The composite flowers of both species first appear in June and blooming continues until the end of summer. Insects, including butterflies, are very fond of these long-flowering plants.