While they don't seem to hybridize nearly as freely as Phoenix, "the Archies" species definitely appear to cross once in a while.
Pictured here is what appears to be a cross between A. cunninghamiana and A. alexandrae.
This palm now (as of September 15, 2009) stands about 25 feet (8.3 m) tall, with a three-foot-long (1 m) crownshaft, and a crown of leaves about 8 feet long (2.6 m) apiece. It was planted on July 3, 2003, from a 32-gallon garbage can used as a pot, and it was about 3.5 feet (1.1 m) tall when planted. It frankly looked like a sad sack with a big divot taken out of the base of the trunk. I don't have a clue where or from whom I got it.
This palm clearly has characteristics of both the King Palm and the Alexander Palm. It has light purple flowers, red seeds, and a brownish crownshaft, like a King. However, it also has light silvery leaf reverses and a very obvious "flare" at the base of the trunk like an Alex.
Whatever it is, it's loving life and living like Charles Darwin commanded: Be fruitful, multiply, and be fit! At least it's trying mightily. Every single leave sheath that drops from the crownshaft reveals a flower bunch that opens immediately, which the honeybees attack en masse, and which gives rise after a few months of orgiastic clumps of seeds, like the familiar red gumballs on a King Palm.
However, one thing this "King Alex" isn't doing is begetting a carpet of seedlings at its base, in spite of my cavalier hygiene habits. The germination rate appears quite low. Experiments are in order to find out more.