In researching Xamarin, what has become apparent is that while the logic aspect is unified, the UI is the part that is segregated albeit there are some wrappers that handle that unify some controls. Here is a Sheet of the App controls across the different environments procured from the Xamarin blog.
Click the below pick to open the full size PNG.
Another Great cheat sheet comes from Cheahengsoon's site which details the different frameworks for UI controls across environment. Possibly some repeated info above but still good to know.