The genus of Citrus loves to hybridize. Most modern grocery stores will carry at least 5-10 citrus fruit, and larger stores may have many more. As it happens most of these are not naturally occurring species, but hybrids, and as it happens, there are only a few base fruit that have been used in the most popular hybrids: the mandarin orange (Citrus reticulata) from China, the citron (Citrus medica) from India, and the pomelo (Citrus maxima) from the islands off Southeast Asia.
While the pomelo is best known for being the ancestor of the grapefruit, this is in fact the result of a double hybridization -- first the pomelo was crossed with the mandarin orange to create the common sweet orange, and then crossed again with the pomelo to make the grapefruit. Likewise, the pomelo was crossed with the mandarin orange to create the bitter orange (aka the Seville orange), which was then crossed with the citron to create the lemon, which was then crossed again with the grapefruit to create the imperial lemon.
As you can see, tracing these lineages can be difficult, and with dozens of hybrids each with multiple cultivars (e.g., the navel orange, the Valencia orange, and the Hamlin orange are all types of sweet oranges), it can be overwhelming to know what is what. However, some of the more familiar descendants of the pomelo include:
- The sweetie (aka the Oroblanco grapefruit), which is another cross between the pomelo and the grapefruit.
- The tangelo which is a mandarin/pomelo/grapefruit mix.
- The Jamaican tangelo, commonly known by the brand name the uglifruit, is also a mandarin/pomelo/grapefruit mix.
- The Tangor and many various off-shoots, including clementine and cutie are a cross between the sweet orange and the mandarin.
- The lime is a loose collection many related fruit, and no clear definition can be given; however, as noted above the lemon is a pomelo/mandarin/bitter orange/citron mix, and the most familiar lime seen on grocery shelves in America is a lemon/key lime hybrid. (A key lime is a hybrid twixt a citron and a previously unmentioned species, the biasong or samuyao (Citrus micrantha) from the southern Philippines).
Fruit development is an ongoing project, as seen by a number of brand names (Cutie, Ugli) sneaking into the above list. The pomelo will continue to help give is many interesting fruits in the decades to come, and whether or not you know the fruit by name, taste, or appearance, you certainly know its descendants.