Cirsium palustre, the marsh thistle, is a herbaceous biennial (or often perennial) flowering plant in the family Asteraceae. It is native to Europe, where it is particularly common on damp ground such as marshes, wet fields, moorland and beside streams. In Canada and the northern United States it is an introduced species that has become invasive. It grows in dense thickets that can crowd out slower-growing native plants. Cirsium palustre can reach up to 2 metres (7 ft) in height. The strong stems have few branches and are covered in small spines. In its first year the plant grows as a dense rosette and in subsequent years a candelabra of dark purple or occasionally white flowers, 10–20 millimetres (0.4–0.8 in) with purple-tipped bracts. In the Northern Hemisphere these are produced from June to September. The plant provides an important source of nectar for pollinators. This C. palustre flower was photographed in Niitvälja, Estonia.
