You can try just about any kind of greens in your soup.
Start out with a clove a garlic in some olive oil and simmer. Add some chopped herbs such as basil and simmer for about 5 minutes.
I use low sodium v-8 juice, one large or 2 small and I add a small can of tomato sauce. I then add a cup of water, but if you like a thicker soup, add a small can of tomato paste or do not add the water. I like this soup thin because I put in a lot of greens.
With the additional spices above, the sauce need nothing else.
I then add 2 small potatoes chopped, an apple chopped and 1/2 cup fennel chopped. You may also add a teaspoon of sugar or agave if the greens you choose are not sweet.
I add whatever greens I enjoy such as collard or mustard green, or spinach.
You can also add some grains such as amaranth or quinoa if you like.
Simmer for about 20 minutes and serve.
I like the soup to sit for a day in the refrigerator. The taste is better.