Yet Another Eurasian Flower Spotted in the Comox Valley

At this time of the year it’s very difficult to find anything in bloom. Fortunately (and I say that tongue in cheek in this case) there are still a few introduced members of Asteraceae in bloom that can be counted on to add a bit of colour during an otherwise dreary West Coast fall day.

Spotted Knapweed (Centaurea stoebe ssp. micranthos) Flower
Spotted Knapweed (Centaurea stoebe ssp. micranthos) flowers are thistle-like in appearance and have an involucre of overlapping black-tipped bracts.

We had some sun in the Comox Valley today and I took the opportunity to take a short lunch time walk in search of flowers. I work at a location that is rural and surrounded by farm fields so looking for introduced plants wasn’t too difficult. In the parking lot I came upon a thistle-like plant that was still in flower. While the purple flower definitely suggested thistle, the leaves lacked the spines that I normally associate with members of Cirsium. I also noted the greenish/gray colour of the leaves and their felt-like texture.

Back home I dug into Plants of the Pacific Northwest Coast and looked at the thistles but nothing looked right – the absence of spines on the leaves eliminated those plants from consideration. Considering the look of the plant and its location in an area of farmland I thought that a logical identification could be a knapweed, however none were listed in my guidebook. Knowing that knapweed is a troublesome weed in the Okanagan I consulted my copy of Plants of Southern Interior British Columbia and sure enough – my mystery plant was spotted knapweed (Centaurea stoebe ssp. micranthos).

More common in the dry farmland of interior British Columbia, spotted knapweed has purple to pinkish disk flowers (no ray flowers) which are generally solitary to few at the end the angular branches. Involucre bracts of the flowers are tipped with black giving them a spotted appearance and its common name. The leaves are pinnate (somewhat fern-like) and greyish-green in colour with whitish hairs that create a felt-like look. Originally introduced from Eurasia, it is widespread in British Columbia and can be found in all sorts of disturbed areas like ditches and road and field edges.

Spotted Knapweed (Centaurea stoebe ssp. micranthos) Leaf
Spotted Knapweed (Centaurea stoebe ssp. micranthos) leaves are greyish/green in colour and felty in texture.

Spotted knapweed is highly invasive and produces about 400 seeds per flower, 14 000 / m2. It can quickly spread through open areas and displace naturally occurring grasses. Currently, 40 000 hectares (100 000 acres) in British Columbia are infested with knapweed. There is potential for the plant to occupy up to 1 million hectares (2.7 million acres), mostly in the southern interior of the province, if it is allowed to spread unchecked. Spotted knapweed should be observed with care as it can cause skin irritation if handled without proper protection.

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