Pioneer violet is the cheerful little groundcover you need in your moist, shaded areas. Bright yellow flowers scattered throughout low-growing heart-shaped leaves liven up those darker corners of the yard. In western Montana you'll typically find it along shaded streams.
 
This is truly a 'set it and forget it' type of groundcover; the prolific little plants shoot their seeds around and before you know if you'll have a thriving violet colony. I guess that's where the pioneer moniker comes from.
 
Like Canada violet, they really do need a fair amount of moisture to thrive, and seedlings that pop up where they aren't wanted can be controlled by not watering them. Personally I want them everywhere. Fun fact: after doing some typical flowers, this violet will make closed-up self-pollinating flowers later in the season that don't look like much but provide an extra round of seeds. 
 
Pioneer violet provides a good base layer for taller shade plants like merten's sedge, large-leaf avens, and shrubs like dogwood, sticky currant, and inland gooseberry. Note: while woodland violet and wild strawberry enjoy the same conditions, if you plant them together the strawberry will generally win because it's a little taller.