Arctium tomentosum (Cotton Burdock) - photos and description

Arctium tomentosum

Arctium tomentosum

Arctium tomentosum

Arctium tomentosum
"Flowering heads densely tangled with an arachnoid tomentum" - from Plants of Riding Mountain National Park

Arctium tomentosum

General: Large, coarse biennials with a branching growth habit and broad leaves.

Flowers: Many globose flower heads in panicles. Flowers discoid only (no ray flowers), corollas reddish-purple, we measured flower heads to 25 mm diameter. Involucres covered in a cottony web.

Leaves: Huge, ovate with a cordate base, alternate, wavy-margined, reduced in size upwards. We measured a leaf at 40 cm long and 30 cm wide.

Height: Height listed in Flora of Alberta to 120 cm, we measured plants to 125 cm tall.

Habitat: Waste places, moist woods, and stream banks.

Abundance: Checklist of the Vascular Plants of Saskatchewan lists the plant as uncommon.

Origin: Introduced.

How to identify this species of Arctium: Might be mistaken for Arctium minus. However, the bracts of the involucre of Arctium tomentosum are densely cottony, whereas with Arctium minus the bracts of the involucre are sometimes slightly woolly (Budd's Flora).

When and where photographed: Photos taken August 10th along a roadside crossing a creek, boreal forest, Duck Mountain provincial park, about 300 km northeast of our home in Regina, SK.