professor-buffalo:

This
beautiful member of the buttercup family (ranunculaceae) is known as Poison
Larkspur (delphimium trolliifolium). While those violet-blue flowers are quite
lovely, this plant does contain a toxin that can cause death. In the Willamette
Valley of Oregon, wooded stream banks
are lined with patches of Poison Larkspur which bloom during the early
part of May.