The Grapefruit Family Tree
I was going to post this in repsonse to Gregor Mendel's comment to the Google queries post, but it was sufficiently cool I thought it rated its own post:
The History of Red Grapefruit, courtesy of Texas A&M.
I thought the coolest part was the family tree at the top...I also liked the red/yellow chimera down at the bottom (In fact, I'm going to swipe that photo and make it the Image of the Day.)
A few things I noticed which relate to previous conversation:
Apparently mutation breeding in Texas was performed by irradiating 'Ruby Red', which produced the experimental line, A&I 1-48. A budsport of A&I 1-48 with darker red fruit became the commercially successful 'Rio Red'. I've heard that a lot of what is marketed as 'Ruby Red' these days is in fact 'Rio Red', but they use the other because of the better name recognition (I don't remember where I heard this, so I have no idea if it's true). It seems A&I 1-48 produced a variety of other red sports as well, though I don't know whether any have been released as cultivars...a further sport of 'Rio Red' was named and released as 'Texas Red'.
'Star Ruby' appears to be the seedless result of irradiating 'Hudson' budwood, so there's an example of mutation breeding successfully producing seedlessness in grapefruit, though it's still not a mandarin.