Spotted Knapweed (Centaurea stoebe)

Spotted Knapweed (Centaurea stoebe)

Many plants, particularly herbaceous ones, are most easily identifiable when in flower. As we move further into the cold season, and flowers (and many leaves) are essentially absent, it seems like herbaceous plant identification should be impossible. While it can be tricky, many plants have such distinctive seed heads or stalks, that they are identifiable well into the winter. While it’s possible to identify many herbaceous species through their winter characteristics alone, I find that now is one of the best times of year to get a sneak peak at plants’ winter appearance, while some vestiges of their summer features still remain – you essentially have two times the number of characteristics to check for, and you have the surety that a particular flower and a particular dried plant are indeed one in the same.

One great example of this right now is spotted knapweed (Centaurea stoebe). Many spotted knapweed plants still have a blooming flower or two despite most of the plants having already dried up for the season. The flowers resemble tiny pineapples topped with a showy spread of pink to light purple, highly dissected petals. The bract tips of the base (“pineapple”) are dark and fringed at the tips, producing a spotted look for which the plant is named.

Spotted knapweed flower resembling a “tiny pineapple” topped with showy pink-purple petals. 

The highly dissected petals of a spotted knapweed flower in bloom. 

Alternatively, you can investigate the dried portion of the plant, which retains its distinctive fringed bracts where the flowers used to be. Evaluating the overall growth form of the plant, as well as the habitat in which it’s found, can also be helpful in winter identification. Spotted knapweed is often much branched and rather scraggly in form and is generally found poor soils, waste places, and edges of roads.

Dried bracts from spotted knapweed flowers. 

Much branched growth form of the spotted knapweed plant. 

Although a great study case for learning “winter weeds”, it is worth noting that spotted knapweed is a European invasive and has become established in much of the United States. In fact, it is listed as noxious, prohibited, banned or otherwise regulated in 16 states. Individual plants generally live between 3 and 7 years, but can live up to nine years and regrow from buds on the root crown, which makes them fairly persistent. They are also prolific seed producers, with individuals generating between 500 and 4,000 wind-dispersed seeds each year, and they produce a deep taproot, allowing them to capture moisture and nutrients even in poor soil. Spotted knapweed’s longevity, fecundity, and other useful adaptations have greatly facilitated its spread in America.

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