Tom's Blog

Sunday, August 30, 2009

Pasture thistles

This is the time when the pasture thistle (Cirsium discolor) is in full bloom. The goldfinches love them. (One year we even had a nest in one!) Right now we have lots in bloom in our planted prairies, with some also in bloom in the more open savannas.

I love the delicate color of this thistle's flowers.

The photos here were taken in a dryer part of the Crane Prairie, where there are lots in bloom. Once a plant gets started flowering, it keeps it up for quite a while, as new buds keep developing and opening.

I have been told that goldfinches do not start mating until the thistles are in bloom. Thus, in contrast to most other bird species, they don't start raising their young until summer is almost over.

This thistle is a biennial, which means that once it flowers the plant dies. Thus, seed set is important in the maintenance of this species. However, seed production is prolific, so there is no problem with its survival. It is just that you never know exactly where next year's plants will appear.


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