- Cirsium palustre is an herbaceous biennial that can grow from 4-5 ft. (1.25-1.5 m) tall. The glabrate stem is winged and armed with spines that result from its decurrent leaf bases. Much of the plant is covered in long, sticky hairs.
- The leaves are spiny and pinnatifid. They are linear-oblong in shape and have tufts of hairs on the lower surface. The lower leaves are 6-8 in. (15-20 cm) long.
- This plant usually has many purple flower heads borne on short peduncles that do not reach more than 0.4 in. (1 cm) in length. The ovoid involucre is 0.4-0.75 in. (1-2 cm) across. The bracts are not spine-tipped. The flowers appear in June and July.
- The mature pappus is white and 0.4 in. (1 cm) in length or less. The small, straw-colored achenes are 0.1 in. (3 mm) long.
- Ecological Threat
- Cirsium palustre grows best in moist acidic soils. It can be found in any disturbed areas as long as its moisture requirements are met. It is common on roadsides and in wet ditches. It is also somewhat shade tolerant, and therefore can be found in moist woods. A combination of wind dispersal and intermediated shade tolerance makes Cirsium palustre a threat to moist, minimally managed habitats.