Tom's Blog

Wednesday, July 30, 2014

Blazing star and swamp milkweed

After a while one gets bored with the masses of mid-summer yellow prairie flowers, which makes the purple species that are coming along now especially welcome.

One of the great species is prairie blazing star (sometimes called gay feather) (Liatris pycnostachya). I have seen whole fields of it, but I find it more attractive as a focal point in a prairie. It  has a fairly wide range, from mesic through wet-mesic to wet. Although it forms corms which can be dug and divided for replanting, it is fairly easy to get started from seed. In a new prairie planted from a seed mix, it usually takes about 3 years to start showing.

This is a western Great Plains species, and is found from the Dakotas south to Texas and east to Indiana. In Wisconsin it is only found south of the Tension Zone. (The Tension Zone, first characterized by Curtis in his work on the Vegetation of Wisconsin, is a wide S-shaped boundary that separates northern from southern Wisconsin.)

One of the interesting characteristics of species of the genus Liatris is that they bloom from the top down, in contrast to most flowering plants. The photo here shows two stalks in the early stages of  flowering. According to Cochrane, since bee pollinators visit the bottom flowers of a stalk first, this method of flowering ensures that the young flowers are visited first.

The other reddish or purple-flowered species that is now in full bloom is the swamp milkweed (Asclepias incarnata). This is only found in wet places, and occurs at Pleasant Valley Conservancy only in our wetland where standing water is present or nearby. The best place to see this species is along the lane that separates the Crane Prairie from the wetland. Individual plants tend to be widely scattered.

The milkweeds have a complex flower structure and pollen is carried in special structures called pollinia. Bees are the principal pollinators and by chance a pollinium will get attached to an insect leg and be carried to another plant. Because of the complex pollination system, only a few flowers on each plant will get fertilized and form seed pods. (There are several potential seed pods starting to form in the photo below.)

Swamp milkweed (Asclepias incarnata) growing at the wet edge of the Crane Prairie. 

Swamp milkweed is fairly easy to do experimental work with and hence has been the favorite species for research on ecology, evolution, and genetics. (Wyatt R. S. B. Broyles 1994. Ecology and evolution of reproduction in milkweeds. Annual Review of Ecology and Systematics 25423-441.)


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