Nuts

A nut in botany is a simple dry fruit with one seed (rarely two) in which the ovary wall becomes very hard (stony or woody) at maturity, and where the seed remains unattached or unfused with the ovary wall. Most nuts come from pistils with inferior ovaries and all are indehiscent (not opening at maturity). True nuts are produced - for example - by some plants-families of the order Fagales. Note that not all true nuts are edible; some e.g. birch, alder, hornbeam, wingnut) are too small to be worth eating, while others (e.g. tanoak) are too bitter to be edible.

--- Wikipedia