From what I've read, wild plant are usually higher in nutritional value than cultivated plants.
Stinging nettle is so high in nutrients that it's used medicinally as a vitamin/mineral supplement, often recommended for pregnant women.
Lamb's quarters has several times the vitamin A of spinach. Autumn olive berries have 17 times the lycopene of tomatoes. Purslane is rich in omega 3s.
I'm writing mostly from memory here, of things I read long ago, but those are ones I remember as being outstanding.