Help me ID this Viola - Garden Specimen Pics

Can you help me ID this viola? I bought it a few years ago for a spring sun, summer shade garden and remember it being called African pansy, the trouble is this plant doesn't resemble the plant of the same name when compared to photos online. These leaves are very heart shaped like a puffy heart and the underneath is purplish. It is unaffected by slugs, readily self sows, and as this past winter has proven, can withstand heavy snow and weeks of below freezing temperatures. I've never fertilized them. The few plants I purchased grow in a mound eight to ten inches high and have seeded dozens more and about one in ten have light green leaves and a more upright than mounded habit. They didn't flower this year until I brushed away the leaf mulch but then performed better than ever. I would really like to know what I have here so if the picture or description rings a bell for you please drop
me a message. I will add more photos later. Thanks and hope are are enjoying your spring!

Below are some pictures of the plants growing in the garden. I originally planted 3 r four plants, all along the far edge of the garden just before the hill drops off. Now, as you can see, there are lots of them scattered about.

Throwback or hybrid, lighter more 'viola' looking leaves and a lighter purple color flower.

A self seeded plant of the originally planted variety.

Here you can see the darker original alongside the lighter throwback/hybrid.



Here (easier to see if you click on the photo for the larger view) you can see the self seeded plants (and the weeds I've yet to pluck).