Marsh plume thistle is a biennial tap-rooted forb growing up to two metres tall with a cluster of large purple-pink flowers and bracts with large spines.

Biennial

Marsh plume thistle grows on moist to wet areas on most soil types, provided seepage is present. Typically, this species grows in unshaded sites but can tolerate some shade. Marsh plume thistle can invade undisturbed riparian areas and moist pastures and reduce or eliminate native vegetation and reduce ecological functioning in these sensitive sites. This species generally does not pose a risk to agricultural crops as it does not tolerate cultivation but may pose a risk to forestry plantations by overtopping and then pressing and/or shading seedlings.

Marsh plume thistle reproduces exclusively from seed dispersed by wind, water, or birds. Seeds can travel large distances, especially in area with strong consistent winds. It is unknown how long seeds remain viable in the soil.

The present occurrence of Marsh plume thistle in the Cariboo Chilcotin Coast is limited to areas north, west, and east of Quesnel. Numerous sites exist near Blackwater Road east of Quesnel and along several Forest Service roads between Quesnel and Wells. A significant amount of Marsh plume thistle occurs east of Prince George in the McBride area where it has been extremely invasive.