PlantFiles: White Sapote, Mexican Apple
Casimiroa edulis

A tropical as hardy as any Avocado. Drought tolerant,and in the Bay Area is a glossy green,dense and compact(Suebelle) tree. On the downside, is it is very susceptable to scale-thanks to the Argentine ants,and a black fungus from scale exudations. Deep rooted,and long lived tree.
EDIT 2008..I just had a fantastic crop this year!!..sweeeet fruit all late spring though even now-October!
If you want good fruit they need a steady supply of water..deep watering once a week is good also. Actually, the skin isn't half bad..better if you peel it,but I don't bother. I think it's the most delicious fruit I have ever tasted. Like vanilla custard. And everbody loves vanilla-right?

White Sapote grows well in Phoenix Arizona, but needs a bit of babying in the beginning until it gets its roots. I have written an article detailing care for this tree in Phoenix.

http://www.phoenixtropicals.com/whiteSapote.html

Popular fruit tree of Mexico and Central America. This tree, though called a white sapote, is not in the Sapote family. It produces large amounts of an apple-sized pale green fruit that has an incredibly sweet and soft fruit in the center (when ripe). The peels are NOT good, so usually the fruit is picked hard, left to soften and eaten with a spoon about 4-7 days later- very good! Tree itself is not all that attracive in my zone (9b) where the leaves tend to brown tip, but is relatively nice in a 10a or better zone where the leaves are more glossy and new growth shows a nice maroon coloration- has good hardiness in Southern California and not sure why it's not grown more.