'Blue Streak' violet willow was featured on Botany Photo of the Day ten months ago, so I encourage you to (re)read the entry for Salix acutifolia 'Blue Streak' in early April of 2005.

The species is native to northern Europe and Asia; this cultivar was selected from plants in Russia, apparently sometime in the late 19th century (I haven't confirmed this against a Salix cultivar reference). Like all members of the genus Salix, the bark of the species contains salicin, a chemical from which the medicinal salicylic acid (important in skin care) and acetisalicylic acetylsalicylic acid, or aspirin, can be derived.

Natural history resource link: The Canadian nature observation program, PlantWatch. “The PlantWatch program enables 'citizen scientists' to get involved by recording flowering times for selected plant species and reporting these dates to researchers through the Internet or by mail. When you submit your data electronically, it's added instantly to Web maps showing bloom dates across Canada, so your observations make a difference right away!”