In plant systematics Epidendroideae is a subfamily of the orchid family, Orchidaceae. Epidendroideae is larger than all the other orchid subfamilies together, comprising more than 15,000 species in 576 genera. Most Epidendroid orchids are tropical epiphytes, typically with pseudobulbs. There are, however, some terrestrials such as Epipactis and even a few myco-heterotrophs, which are parasitic upon mycorrhizal fungi. The Epidendroideae are difficult to classify. They have been divided in “lower epidendroids” and “higher epidendroids”.