How did everyone do with last week’s riddle? Jumping on the burdock trend, this time around we have another classic invasive for you! With a brutish appearance and an army of sibling invasives, this I Spy feature might be one of the easier guesses.
Diffuse Knapweed (Acosta diffusa) is a biennial or short-lived perennial that was brought to North America as a hay contaminant in crop seeds, from the Eastern Mediterranean. This spindly invasive can grow between 0.1- 0.6 m tall and has a single, erect stem with multiple branches, covered with stiff, white hairs. Its small, white (sometimes light pink or purple) flowers form in either small clusters, or individually, on the end of branches. Leaves are stalkless, rough, hairy, and divided, becoming bract-like near the flowers!
Although this resilient weed can be highly drought tolerant, it’s actually quite sensitive to any excess in moisture! Diffuse Knapweed grows best in disturbed, dry, sandy areas such as grasslands, pastures, woodland clearings, and roadsides. This unpleasant invasive causes foraging issues on rangelands by out-competing the more desirable plants, and spreading rapidly. Not only that, but Diffuse Knapweed has been found to reduce soil erosion along streambanks and marshlands, as well!
Be aware, there is a Diffuse Knapweed look-alike that’s also invasive, and can be found in the Sea to Sky Region. Spotted Knapweed (Centaurea bierberstienii) has hairy, deeply-cut leaves, with the lowermost leaves presenting a black-tipped fringe, giving it a “spotted” appearance. Flowers are purple, and on occasion, white, growing on a single or multiple upright stems that can be 1 m tall.
This devious plant is categorized as “contain” under SSISC’s Species Priority List for the Squamish and Whistler regions, and “strategic control” for Pemberton. That means we have to take extra care to prevent it from spreading into new territories! Think you’ve spotted Diffuse (or Spotted) Knapweed? Report it here or email us at firstname.lastname@example.org.