Tradescantia occidentalis, or prairie spiderwort, is a perennial monocot found in central North America. Although it has a fairly widespread distribution, there are only four known populations of this species in Canada, where it is listed as threatened by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Prairie spiderwort grows in grasslands and on partially-stabilized sand dunes. In Canada, suitable habitat occurs only in the southern parts of the prairie provinces: Alberta, Saskatchewan, and Manitoba.
Tradescantia occidentalis has semi-succulent stems and narrow-bladed leaves. The 3-petaled flowers grow in a raceme of up to 10 flowers, which can be pink, white, violet, or most commonly, dark blue as shown in today’s photo. The bright yellow anthers contrast beautifully with the deep blue of the petals and the blue-hair decorated filaments. Some sources claim that the spider-like appearance of these hairy filaments give spiderwort its common name, while others attribute the name to cobweb-like strands that form from a sticky fluid when the leaves or stem are broken.
The habitat required by Tradescantia occidentalis (PDF) is quite specific. Sand dunes must be fairly stable, yet also must have some bare patches where seedlings can become established, as prairie spiderwort only reproduces by seed. Historically, regular fires and disturbance by ungulates routinely created patches of bare sand for Tradescantia occidentalis to colonize. Now, Canadian management plans call for rangeland management practices and prescribed fire to create the levels of disturbance needed by this species.
You may be wondering, if population levels of Tradescantia occidentalis are healthy through most of its range, why worry about a few small populations in Canada? A report by David Fraser, titled Species at the Edge: The Case for Listing of “Peripheral” Species (PDF), does a good job of explaining some of the principles that guide ecologist’s concern for peripheral populations. One of the numerous arguments presented by Fraser is that individuals growing in marginal habitats are exposed to higher selective pressures, and are usually genetically distinct from core populations. This genetic diversity may prove to be an important factor in the long-term survival of a species.