The orchid family – one of the most species-rich plant families on earth – contains over 200 fully mycoheterotrophic species. Most green orchids are dependent on fungi during part or perhaps all of their life cycle.
Classification: Monocots, Asparagales
Genera with mycoheterotrophic species: Cyrtosia, Erythrorchis, Galeola, Lecanorchis, Pseudovanilla, Arthrochilus, Brachycorythis, Brunettia, Chamaegastrodia, Corybas, Cryptostylis, Cystorchis, Danhatchia, Degranvillea, Odontochilus, Platanthera, Platythelys, Rhizanthella, Aphyllorhis, Auxopus, Cephalanthera, Corallorhiza, Cremastra, Cymbidium, Didymoplexiella, Didymoplexis, Dipodium, Epipogium, Eulophia, Gastrodia, Hexalectris, Kalimantorchis, Limodorum, Malaxis, Neottia, Pogoniopsis, Risleya, Silvorchis, Stereosandra, Tropidia, Uleiorchis, Wullschlaegelia, Yoanina, Vietorchis, Yunorchis, Danxiaorchis
Diversity: Orchidaceae are usually considered to be the largest family of flowering plants with ca. 22,000 species in about 880 genera. Circa 235 species in 45 genera are leafless and are putative full or nearly full mycoheterotrophs. The largest genera of full mycoheterotrophs are the Old World Aphyllorchis (33 species) and Gastrodia (22 species). Partial mycoheterotrophy has been detected in many green-leaved species (e.g., Cephalanthera spp., Cheirostylis montana, Cymbidium spp., Epipactis spp., Ophrys insectifera, Platanthera bifolia) and may be relatively common in terrestrial orchids. Occasionally achlorophyllous “albino” individuals are found in some otherwise partially mycoheterotrophic species, notably in Epipactis and Cephalanthera. Some terrestrial orchid species have separate vegetative and leafless flowering stages, and have been misinterpreted as mycoheterotrophs.
Distribution and habitat: Orchidaceae have a worldwide distribution, occurring in almost every habitat on the planet and absent only from the polar regions and the driest of deserts. The great majority are to be found in the tropics, mostly in Southeast Asia and in the Neotropics, and their diversity peaks in montane tropical regions where abundant rainfall allows for the maximum growth of epiphytes. Most fully mycoheterotrophic orchids are found in the tropics, but their diversity has a highly uneven distribution. The vast majority of tropical myco- heterotrophic orchids occur in Southeast Asia and adjacent Australasia. In contrast, the floras of tropical Africa and particularly the Neotropics are surprisingly poor in fully mycoheterotrophic Orchidaceae. A majority of orchids are perennial epiphytes, which grow anchored to trees or shrubs in the tropics and subtropics. Other species are terrestrial or lithophytes, growing on rocks or very rocky soil. Nearly all temperate orchids are terrestrial. All mycoheterotrophic orchids are terrestrial, although some species, such as Erythrorchis cassythoides, are climbers.
Fungi: Mycoheterotrophic orchids grow on ectomycorrhizal and saprotrophic fungi.
Fun fact: The ghost orchid (Epipogium aphyllum) can disappear for up to 30 years between successive flowering episodes at the same site.