Northern Prairie Wildlife Research Center
ASTER FAMILY (Compositae or Asteraceae)
IND. STATUS: OBL
FIELD CHARACTERISTICS: A biennial herb 50-200 cm. high. Leaves are pinnatifid, green beneath and have weak spines. A basal rosette is formed the first year, and an unwinged flowering stalk the second year. The flower head does not have stiff spines as in most other thistles, but instead is weakly spined and sticky because of a gummy resin. Flowers are pink to purple. In flower from July to October.
ECOLOGICAL NOTES: Swamp thistle is characteristic of calcareous fens, and also occurs in wet to wet-mesic prairies and sedge meadows that are supported by groundwater seepages. Another common name is fen thistle.
SOURCE: Gleason and Cronquist (1991); and Swink and Wilhelm (1994).