Actually there are about 750 different rhododendron species in a genus that ranges from tropical plants to arctic plants and covers the full spectrum of colors. They cover the range from dwarf to trees. The can be found from sea level to the Himalayan mountains. They can be found in Europe, Asia and North America. They can be found from the equator to Lapland.

In addition there are many thousands of hybrids these species that combine the best characteristics of several plants into a new plant.

Here is a link that might be useful: rhododendrons