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Depending on the taxonomic system used, all genera with monotropoid mycorrhizas are found either in the family Monotropaceae or in the clade Monotropoideae, in the family Ericaceae. Regardless, 10 genera are presently recognized, all but 3 of these genera being monotypic, i.e., with only one species. The Asian genus Cheilotheca has four recognized species, and the genera Monotropa and Pleuricospora each have two species. The distribution of the group is primarily north temperate, with the largest number of species in western North America. Most of the research, in terms of mycorrhizal associations, has been with the genera Monotropa (Indian pipe), Sarcodes (the snow plant), and Pterospora (Pine drops). All species are non-photosynthetic and therefore myco-heterotrophs, depending on fungal links with photosynthetic trees or shrubs for carbon compounds.
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