Swamp Thistle

A biennial or short-lived perennial, swamp thistle (Cirsium douglasii) is also commonly known as Douglas’ thistle. This native is found in wet places in Oregon, California and Nevada.

Swamp thistle has one to several woolly, branching stems. The hairs on the greyish leaves are tomentose (intertwining). The longest leaves are basal while the cauline (stem) leaves are smaller. The basal leaves have a spiny petiole and are deeply lobed or may be toothed. The bases of cauline leaves are expanded ear-like around the stems and spiny along the margins.

A cluster of flower heads surrounded by small leafy bracts occurring at the tips of branches form the swamp thistle inflorescence. Each flower head is composed of white to purple disk flowers. The phyllaries (bracts surrounding the flower head) have a sticky, resinous midrib ridge and can be purple-tipped.

Swamp thistle fruits are a dark achene with a long pappus.

Like all members of the Cirsium genus, swamp thistle is edible. The peeled leaves and stems can be eaten raw or cooked as a potherb. As a child I was constantly picking and peeling Cirsium stems to nibble as I played in the woods. The stems tasted like and had the texture of celery. Native Americans utilized Cirsium species to treat a variety of maladies from stomachache to diabetes, respiratory infections to parasitic infections.

These swamp thistles were photographed in August along the Pacific Crest Trail in Warner Valley near Drakesbad, Lassen Volcanic National Park CA.

This entry was posted in Wildflowers and tagged , , . Bookmark the permalink.