Quantity, quality and dispersal distance of wind-blown achenes and pappi were determined during the peak time of
dispersal over twelve site-years in Minnesota during 2006 and 2007. Approximately twice as many pappi than
achenes were trapped. Wind blown pappi tend to travel near the ground. Most achenes fell near the parent plants
and their population density declined exponentially with increasing distance. Over 80% of pappi collected did not
have an achene attached. Concomitantly, seed production in Canada thistle was monitored for 8 site-years in
Minnesota. Averaged across years and locations, female Canada thistle shoots that flowered produced an average
of 38% empty, 17% shrunken, and 44% normal achenes. Male shoots produce about half the number of seedheads
compared to female shoots. A low level of hermaphroditic expression was observed in male shoots. Though seed
production by female Canada thistle is extremely variable, when sufficient pollen is available, Canada thistle
clearly has the potential to generate significant contributions to seedbanks to maintain invasive stands. However,
dispersal by wind is for the most part, local. Long distance dispersal of significant numbers of healthy achenes
would be a rare event.
Becker, R.L.; Haar, M.J.; Kinkaid, B.D.; Klossner, L.D.; Forcella, F..
Production and Wind Dispersal of Canada Thistle (Cirsium arvense L.) Achenes.
Minnesota Department of Transportation.
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