Direct opposites:
* Terrestrial plant: This is a plant that grows on the ground, in contrast to an epiphyte which grows on other plants.
* Root-bound plant: This emphasizes the difference in how epiphytes obtain their nutrients and water.
Other options:
* Geophyte: A plant that grows underground, emphasizing the difference in location.
* Parasite: While not strictly an antonym, a parasite draws nourishment from a host, unlike epiphytes which are usually non-parasitic.
* Soil-dwelling plant: This emphasizes the dependence of soil for nutrients and water, in contrast to epiphytes.
Ultimately, the best antonym depends on the specific context and the aspect of the word "epiphyte" you wish to contrast.