Complex sentence: Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plants in landscaping in many parts of the world, including both temperate and subtemperate regions, while many species and cultivars are grown commercially for the nursery trade.
Split into simpler sentences: Both species and hybrid rhododendrons (including azaleas) are used extensively as ornamental plants in landscaping in many parts of the world, including both temperate and regions. Many species and cultivars are grown commercially for the nursery trade.