Yatsutko, over at Khrenovina, writes about citrus hybrids.
It turns out that what we recently bought at Iki under the name Sweetie is a hybrid of grapefruit and pomelo.
And the pomelo itself, along with the citron, is an ancestor of all modern citrus fruits. Grapefruit and even lemon are hybrids. And the mandarins we eat are not mandarins at all, but all sorts of suspicious characters, such as hybrids of true mandarins and oranges.