in Thoreau’s Journal:

The epigaea is not quite out.  The earliest peculiarly woodland herbaceous flowers are epigaea, thalictrum, and (by the first of May) Viola pedata.  These grow quite in the woods amid dry leaves, nor do they depend so much on water as the very earliest flowers. I am perhaps more surprised by the growth of the Viola pedata leaves by the side of paths amid the shrub oaks, and half covered with oak leaves, than by any other growth, the situation is so dry and the surrounding bushes so apparently lifeless.