A guide to nonnative invasive plants inventoried in the north by ...

Cirsium arvense
Canada thistle CIAR4
Form: Dioecious perennial 1-4 ft (0.3-1.2 m) tall; plant nearly
glabrous to sparsely hairy. Deep-seated creeping roots.
Leaves: Alternate with a basal rosette, oblong, and
irregularly lobed with very prickly margins. Green on both
sides, glabrous to pubescent underneath. Stems ridged and
hairy.
Flowers/fruit: Purple to occasionally white; heads up to
½ in. (1.3 cm) in diameter, discoid, and 1 in. (2.5 cm) or
less high. Fruit is an achene ⅛-½ in. (2.5-4 mm) long with
a feathery pappus attached to the apex (which lets it float
through the air).
Habitat: Open habitats including prairies, savannas, fields,
pastures, wet meadows, and open forests.
Notes