I once began a list of wild edibles rich in various vitamins and minerals. I realized that I probably was going to a lot of trouble for something a handful of people would read AND apply. Most people don't realize what vitamins and minerals are their regular food, much less wild plants and animals/fish and their products that they hunt and forage for.

Still, to answer the question: what wild edibles are rich in calcium. Almost every leafy green edible is rich in calcium. Now, go do a little basic research so that you can find them in your backyard. Wild strawberries grow everywhere, and while they don't taste that great, they do have a lot of nutrients like calcium.

Remember: Don't gather from along roadways because of concentration in lead from car/truck exhaust.

In a collapse, a lot of people will finally eat salad, a lot of it, in order to get vitamins.
[link to www.thebestofrawfood.com]

Here's a tip: when the white clover flowers come in, harvest them. They can be powdered up into a flour that's rich in protein. Most people won't think to harvest this in a collapse. It doesn't have gluten in it, of course. Only spelt and wheat have that, so it won't rise. It's added to extend your flour.

I'll bet that if you live in many places that have yards, that you have at least 20 plants that you could eat to gain important vitamins. The bad news is that unless you've got a major garden going, you're not going to be able to be a vegetarian. You couldn't gain enough calories and would starve to death without growing a lot of crops, even if gathering everything around you.

I'm not anti-vegetarian at all. In a collapse, it's extremely difficult to gather enough. Even the best gardener would need a huge garden AND livestock to make it as a vegetarian. So vegetarians out there, you especially need to consider how much you need in food supplies.

Meat eaters can eat a lot more from the animal than you're used to in order to maximize your nutrition. It's funny, but people complain about pink slime (hamburger with added in meat-byproducts) but our ancestors would have been greatful for such things. You'll not only be eating sweetbread, but using soup bones to make broths rich in nutrients (re the bone marrow comment). I'd say more, but would probably gross out a lot of people. Very little was wasted on the frontier.

I'd like to encourage all of you to check out Green Deane's videos on wild edibles. He's the nicest person around as well as brilliant. His youtube videos have tons of tips on identification, history, nutrition, recipes, etc. He also discusses harvesting snails, mussels, insects, etc.
[link to www.youtube.com]

Trust me, you can learn to identify wild green plants with relative ease. People in times of old without much education learned them, and so can you.
Be cautious about wild mushrooms; they're always problematic to identify even to experts unless they're morels.