Natural History

Geographical Origin and History

Marsh thistle is native to most of Europe and to western Asia (Gleason and Cronquist 1991, Tutin et al. 1976). It had been introduced in the northeastern US and adjacent Canada by the early 1900s. It was first collected in Michigan in Marquette County in 1934, and has since spread across the Upper Peninsula and into lower Michigan and northeast Wisconsin (Voss 1996, WIS 2002, pers. obs.). Marsh thistle is also spreading aggressively in east-central British Columbia (Martin 2001).

Characteristics

Marsh thistle is a fibrous-rooted biennial or monocarpic perennial (Tutin et al. 1976, Falinska 1997). The species is very spiny, including its winged, spiny stem. Immature plants form a rosette, with a circle of leaves close to the ground. Flowering plants may reach 2 m (6.6 ft) or more tall.

Similar Species

Like marsh thistle, the Eurasian bull thistle [Cirsium vulgare (Savi) Tenore] is very spiny, with a spiny, winged stem. It is usually a stockier plant than marsh thistle, though, and produces fewer, larger, usually solitary flower heads at the ends of the branches (Voss 1996). It is also a more ruderal (disturbed-habitat) species than marsh thistle, and is not as competitive or aggressive in most natural habitats (Gleason and Cronquist 1991, Voss 1996). It favors sunny, dry to moist sites such as roadsides and pastures.

Musk and plumeless thistles (Carduus nutans L. and C. acanthoides L.) are also introduced from Europe, and are invasive in some habitats. Like marsh and bull thistle, Carduus spp. also have spiny, winged stems. They differ from true thistles primarily in having a pappus of capillary (single-filament) instead of plumose (feathery) bristles (Gleason and Cronquist 1991). In the upper Great Lakes region these species primarily invade open, disturbed habitats (Voss 1996).

The native swamp thistle (Cirsium muticum Michx.) occurs in similar habitats as marsh thistle. Unlike marsh thistle, though, the stems of swamp thistle have only scattered short, soft, whitish hairs, and are not at all winged or spiny. The flowerheads are somewhat larger and less numerous than those of marsh thistle. Swamp thistle also tends to be much less gregarious and aggressive than marsh thistle (Voss 1996), frequently appearing in colonies of a few to a few dozen scattered plants.

Reproduction and Dispersal

Reproduction in marsh thistle is entirely by seed (Falinska 1997). In favorable habitats plants usually flower their second year, but under heavy competition or suboptimal conditions plants may remain as rosettes for several years, until they become large enough to bolt (Falinska 1997). Flowerheads are produced from June through July (Gleason and Cronquist 1991, Voss 1996). Numerous plumed seeds are then produced, which may be carried for long distances by the wind. Grime et al. (1988) indicate that marsh thistle forms a persistent seed bank. Disturbance appears to greatly facilitate establishment spread, though plants are capable of invading undisturbed natural areas as well.

Habitat Preference and Tolerance

Marsh thistle prefers moist to wet ground. And it is well-adapted to climates with long, cold winters - in Europe and western Asia it is found as far north as the Arctic Circle (Martin 2001).

In the upper Great Lakes region marsh thistle readily establishes in moist to wet disturbed habitats such as ditches, road and power line corridors, meadows, old logging roads, and recently-logged woods, where it often forms dense, extensive colonies. From these disturbed habitats it readily invades less-disturbed or undisturbed habitats, including open or shaded wetlands, bog edges, and wet woods. While it probably prefers full sun, it is somewhat shade-tolerant and capable of invading nearly closed-canopy forest (Gleason and Cronquist 1991, Voss 1996, pers obs.).