Photo credit: © Rea Brinkhoff/Flickr
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Species at a Glance
Marsh thistle is well-established in northern Michigan and northern Wisconsin and established in a more scattered manner in New Hampshire, New York, Massachusetts, and Maine. It invades a wide variety of wetland and moist upland habitats, including wet meadows/marshes, shrub wetlands, swamps, floodplain forests, bogs/fens, coastal grasslands, forest edge/old fields, roadsides/ditches, mid- and late-successional forests, and lakeshores/beaches. It is capable of invading mature, undisturbed vegetation and forming tall, dense colonies. These abilities combined with the presence of rare species in many invaded habitats constitute the primary threat posed by this species. It is increasing in abundance in the Great Lakes region and appears to be of greater concern to managers there than to those in New England. It prefers moist ground and climates with long, cold winters, so its potential U.S. range may not be much larger than its current range. Management is complicated by the species' strong resprouting abilities, but is usually successful after a few years of persistence.
Look-alike species include Canada thistle (Cirsium arvense), bull thistle (Cirsium vulgare), plumeless thistle (Carduus acanthoides), and swamp thistle (Cirsium muticum).
As a wetland species, marsh thistle perfers to be in areas of moist acidic ground including marshes, bogs, fens, wet fields, stream sides, and forest edges.
The spread of marsh thistle is linked to the spread of human agriculture from the mid-Holocene era or before.
Marsh thistle is currently found in the higher latitudes of North America, including Pennsylvania (where it has been reported in Clinton County).
Marsh thistle forms dense thickets that can crowd out native species. Considered a prolific seed producer, marsh thistle can yield up to 2,000 wind-borne seeds per plant. Resulting impacts to native habitats include a decline in biodiversity and compromised ecological integrity. In areas where rare species exist, marsh thistle poses a significant threat.
Information for this species profile comes from various sources including: