How many different kinds of desert oasis palm trees are there?

I'm not sure how many total species there are, but here's a few that I know of that are found in arid and semi-arid regions of the world: Washingtonia filifera (California/Arizona/Mexico) Washingtonia robusta (Mexico) Phoenix dactylifera (North Africa/Middle East) Phoenix canariensis (Canary Islands) Phoenix theophrasti (Crete) Brahea armata (Mexico) Brahea edulis (Mexico) Brahea brandegeei (Mexico) Medemia argun (Southern Sahara) Nannorhops ritcheana (Afghanistan) Chamaerops humilis (Mediterranean basin) Chamaerops humilis v. cerifera (Morocco) Livistona mariae (Australia) Hyphaene thebaica (Africa)