that send up suckers from the roots of the original rootstock. If not cut out, those rootstock branches sometimes produce fruit, which is bitter, like a Seville Orange. My mother has made marmalade from that fruit a couple of times. There's also a bitter lemon fruit that comes up from another tree as root stalk suckers. Oddly, it makes very good lemonade when diluted and with enough sugar. the bitter lemon has a very thick rind and is about the size of a Valencia orange, the orange variety that is used for most orange juice. The bitter lemon rootstock is also used for grafting purposes.
Of course, there is a constant effort to remove such rootstock sucker branches.
They also grow avocados, and there is a wonderful tree in the orchard that is completely based on the orginal rootstalk. The avocados it produces are twice as large as the Haas variety grown for sale, and has a long neck. It's delicious, but has zero market value, since nobody wants an odd-looking avocado. It's my parents' Guacamole avocado tree.