Centaurea maculosa - Spotted Knapweed

Spotted KnapweedCentaurea maculosa, commonly known as Spotted Knapweed, is an herbaceous perennial with purplish-pink flowers resembling the more commonly known Thistles (both are in the same family, the Asteraceae).  Spotted Knapweed was accidentally introduced to the United Stated in the late 1800's in a batch of Alfalfa seed imported from Asia Minor (Mauer and Russo 1995).  It is also known as a "ballast waif", having been introduced through ship's ballast, and was commonly found growing in areas used to dispose of wool-waste (Fletcher 1913).

Like most invasive plant species, Spotted Knapweed grows well in disturbed areas.  Once it has been established at a disturbed site, it continues to spread into the surrounding habitat.  This species beats out its native competitors by at least three methods: 1) A tap root that sucks up water faster than the root systems of its neighbors, 2) Quick spread through high seed production, and 3) Low palatability, meaning that it is less likely to be chosen as food by herbivores (Mauer and Russo 1995).

Spotted KnapweedThe animated image below shows that Spotted Knapweed was already well-established in the state of Massachusetts by the 1920's.  Although the image shows no published records for C. maculosa in either Essex County, it is highly likely that this species does grow there.  While Spotted Knapweed is not considered a serious problem in Massachusetts, it is a major problem in the Western United States (See Colorado reference below).  Like other species in the Asteraceae family, it has wind-dispersed seeds that can easily be carried into habitats where it may pose a threat to the prosperity of native plants, and has in fact been observed by the author of this page growing on conservation land.

Animated Map of the Occurrences of Centaurea maculosa Over Time
 
(What does this image mean?)


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