I wonder if you actually mean amphibious? Many modern aircraft that can land on water are conversions of land based planes and retain some ability to use hard surfaces as well as water for landing take/off. However, that doesn't mean they use their original undercarriage because the floats are much bigger than the original wheels and, even if the wheels could be left in place they wouldn't reach the ground. So if the requirement is to land on both wheels are fitted inside the floats and they are dangled as required. I gather the landing characteristics of an aircraft so fitted are interesting.
However, even when the plane is a conversion from a land based machine it is sometimes fitted with floats on the assumption that it will never use land. In some cases the floats are interchangeable with landing gear - I remember pitching up at an airfield next to a lake in Quebec and finding rows of floats waiting to be attached to aircraft currently using their wheels.
Then you have purpose built aircraft. Some, like the current CL215/CL415 water bomber are built with both a floating hull and a retractable land undercarriage. Another example is the 2nd world war Catalina. Then, also from the 2nd war we have the Sunderland which was built as a flying boat, pure and simple. To get it out of the water they had to fit special wheels and then pull it up a slipway.
As a side I would also mention the WIGE (wing in ground effect) "things" built by the Russians and affectionately known as the Caspian Sea Monster.