Naval orange?

Perhaps yesterday's blog about scurvy subtly influenced someone to ask about the naval orange.  Of course, it was the use of lime juice to prevent scurvy in the British navy that resulted in the nickname "limey".  However this isn't a naval

nickname at all, it's navel.  Yes, an orange with a belly button.  If you slice a navel orange in half top to bottom you'll see that it's really two oranges, a large one almost surrounding a small one at the apex of the fruit, and the slight protrusion of this 2nd small fruit through the rind of the larger fruit produces the navel (bottom of image) on the apex of the fruit.  [Image courtesy of Brandizzi, Wikimedia Creative Commons] This type of orange has probably arisen more than once, or if just once, this sport, this mutant showed up 200-400 years ago.  In addition to having this double ovary, one on top of the other, the mutation rendered the fruit sterile so it produces no seeds.  Good for the eater, bad for the plant.  Navel oranges can only be reproduced asexually by cuttings or buds grafted onto other root stock.  So no navy involved, and no umbilical scar either really, but let's be careful with those vowels people.  Oh, and this is a fun fact too.  The flesh you eat in citrus fruits is not derived from the ovary wall; the juice sacs are modified hairs (look at one carefully) that fill the locule, the space, around the seeds, if the fruit has any.