Cirsium arvense (L.) Scop.

Family: Asteraceae, Tribe: Cynareae

Pertinent Synonyms & Notes (particularly those used in California; go to GRIN for other synonyms)

Carduus arvensis (L.) Robson, Cnicus arvensis (L.) Hoffm.

Pertinent Common Names (particularly those used in California; go to GRIN for other common names)

Canada thistle

Primary Disseminule Type


Description (diagnostics are in brown)

Fruit a cypsela, oblong, sometimes slightly curved, slightly compressed, cross-section ± elliptic to 4-sided, 2–4 mm long x 0.8–1.5 mm wide x 0.4–0.8 mm thick. Surface glabrous, smooth, somewhat shiny, straw-colored to light brown, sometimes with lighter-colored longitudinal stripes. Pappus easily deciduous as a unit (bristles fused at the base into a ring), bristles nearly equal (12–32 mm long), plumose (cilia 2–3 mm long), tan.

Style base cylindrical, prominent (up to 0.5 mm long), surrounded by a raised and sometimes lighter-colored collar.

Fruit attachment scar basal, truncate, ± flush, whitish.

Similar Species

Cirsium vulgare

Risk Assessment (codes in yellow or red indicate cause for concern; assessments are current as of mid-2011; click AUQP, NZBORIC, or NZBPI for access to the most recent versions of these databases and possible assessment changes)