Knapweed

Centaurea

Imagine a genus with 500+ species in it… Then imagine how intimidating it is to name a flower in this group to species! So in the interest of avoiding an error, I’ll stop at the genus level on this one. The folks at Wikipedia report that all the members of the genus Centaurea share these characteristics:

they are in the family Asteraceae
the leaves at the bottom of the plant are usually divided and become smaller and entire toward the top
across the genus, the flowers of plants in this genus can vary in color: red, pink, blue or yellow
the disk flowers (center of the flower) may be darker than the ray flowers along the margins of the flower
the flowers erupt from a basket-like cluster of scaly bracts
many species are allelopathic, which gives them a competitive advantage; consequently many are considered invasive weeds
common names include: knapweed, centaury, centory, starthistles, basketflower, cornflower
all are ‘copious nectar producers’ that are attractive to pollinators like butterflies and bees
some species, like cornflower (or bachelor’s buttons) are cultivated as beloved ornamentals in gardens

I believe that at least some of the flowers in this gallery are Spotted Knapweed, or star thistle, which is an introduced species that is listed as an invasive plant in much of North America. This biennial or short-lived perennial thrives on disturbed sites. The name “spotted” is derived from the spots formed by black margins on the flower bract tips. The flowers of spotted knapweed are pink to purple and have a cone of bracts below the flowerhead that looks a bit like a basket. I’ve included some leaf images here as well, so if there’s an expert out there that can key these flowers to species, I’d be grateful.

The plants here were photographed in July and August, growing abundantly in abandoned hayfields near Blacksburg, Virginia.