Violets (Viola sonoria, or the common blue violet) grow wild all over my yard. After the dandelions they are the first pop of color in the spring, first with their bright green arrow shaped leaves and then with their cheery violet (not blue, but not purple either, but somewhere in between) flowers. The blooms thrive in the shady spots under trees, along buildings, or next to ledges where they can get some sun, but not too much. Violets do not love to be hot or dry- ever heard the phrase wilting violet? The blossoms are as fragile as they are beautiful, and won't last long if exposed to heat or sun.
Another interesting tidbit about violets- they reproduced both sexually and asexually. Because violets bloom so early in the spring they run the risk of missing pollinators altogether. Not a great survival strategy. But they get around this by also sending out runners to form new plants, which is why violets often grow in large clusters. Violets (other than Viola odorata, or sweet violet, I believe) also have no fragrance, and bees and hummingbirds are less attracted to the muted violet color, so all in all it was a good idea for them to develop a backup plan.
Both the leaves and the blossoms are edible. The leaves are pleasantly spicy and make a good addition to a salad blend, or can be cooked and eaten in place of spinach. I use the blossoms to make a beautiful pinkish jelly every spring. Another fun fact- why is the jelly pink? Violets blossoms are a natural litmus test. Add acid and they turn pink (and the jelly recipe I use calls for lemon juice), add a base and they turn green. I've also used them to color a simple syrup you can use to make fun colored cocktails.
See, super useful, and we haven't even gotten to the medicinal uses.
(oh, btw, go easy on eating the blossoms, they can have a laxative affect)
Nutritionally, the leaves are really high in vitamin C and beta carotene. According to Lise Wolff (who I was privledged to take a plant walk with earlier this fall during a herbal conference) 100g of violet leaf (which isn't a whole lot) contains 20,000 IU of beta carotene (4x the RDA of 5000 IU) and 264mg of vitamin C (roughly 3.5x the RDA of 75mg).
The leaves are slightly mucilaginous, which is something to keep in mind when you first try them- they will be a tiny bit slimy. This is good for you, but also most mucilages break down with heat and time, so after cooking there should be less of a slime factor, and raw the slimy feeling is only a suggestion in your mouth as you chew the leaves. This mucilage makes violet leaf tea excellent for sore throats.
One of the more serious uses for violet is for treatment of any type of fibrous mass, particularly in the breast tissue. I have used it to treat pernicious clogged milk ducts (fresh leaf made into a poultice and applied to the breast, as well as drinking violet leaf tea) but others have seen success with things as serious as breast cancer (this would be an opportune time to say I am not a doctor and I'm not telling you to make any serious decisions, my only goal is to inform).
Overall, violet leaves are just good for you. They are mild enough to give to children for things like headache and fever as they seem to aid the lymphatic system, but they are strong enough to fight tumors. They help support several systems of the body. It has been suggested to me in the past that they are just a weed and I should be pulling them out of my yard.
I'd rather the violets pushed out the grass, because until I get a cow grass is pretty useless to me.
Note: While I talk mostly about Viola sororia, most of this information is generally recognized as being true for all wild growing violets.
Viva Violets! by Lise Wolff
300 Herbs: Their Indications & Contraindications, Matthew Alfs
Edible & Medicinal Wild Plants of the Midwest, Matthew Alfs
Medical Herbalism: The Science and Practice of Herbal Medicine, David Hoffmann, FNIMH, AHG