There is no other way around it--Madagascar is an evolutionary uniquety. 80% of the island's species live nowhere else on Earth. Among this uniqueness is a habitat that seems to come out of science fiction: The Spiny Forests.
These forests grow in the western half of Madagascar, where the mountains that split the island in half bar rain from passing through. These forests can survive months if not years without rain, and the plants have to come up with certain adaptations for such meteorological hostilities. Most are armed with thorns and needles, which help retain moisture loss, whereas others have given up on leaves and instead photosynthesize through their trunks.
The spiny forests of Madagascar are one-of-a-kind, separate from the other rainshadows of the world--the Mojave in California, the Atacama in Chile, the Judaean in Israel, even the deserts of mainland Africa's northern half. But does it have to be? Could spiny forests similar to those in western Madagascar grow in the other rainshadows around the world?
(Side note--don't bring up the saguaro forests of the Sonoran, because saguaros are cacti, not real trees.)