Approximately 40% of living ferns are tropical epiphytes, a fact that supports the hypothesis that:
1. the origin and eventual domination of angiosperms in tropical forests both displaced and created new opportunities for other plant lineages.
2. plant lineages are conservative in their basic ecology and tend to diversify in the same environments in which they originated.
3. epiphytic ferns are all that remain of an ancient diversification of ferns that preceded the evolution of angiosperms.
4. most fern diversity is in temperate forests.