Viola species; Violaceae (violet family)

There are at least a dozen different species of violets in this area.  I’ve found three so far.

Here’s common blue violet (V. sororia):

The next one is the same species; they are known to be either solid blue or white with blue markings:

And here’s round leaved violet (V. rotundifolia):

And here’s downy yellow violet (V. pubescens):

You can’t see the telltale differences without zooming in on the pictures, but round-leaved violet has only basal leaves, and downy yellow has stem leaves (and fine hairs).