The monotropes (Monotropoideae, Ericaceae) are non-photosynthetic plants that obtain fixed carbon from fungi with which they form monotropoid mycorrhizal associations. These fungi in turn form ectomycorrhizae with neighboring photosynthetic plants that likely serve as the original carbon source for the monotropes. We wanted to determine if different lineages of the Monotropoideae are specifically associated with different lineages of fungi. To answer this, we sampled a total of 164 plants from 9 of the 11 recognized species in the Monotropoideae. We have obtained fungal mtLSU and nrITS sequence data from their mycorrhizal associates. To identify the fungi, sequence data were obtained from 97 basidiocarps. In addition, we obtained plant nrLSU and nrITS sequence data for the monotropes. All monotropes were highly specialized, but host-jumps to distantly related fungi have occurred several times. The snow plant (Sarcodes) associates exclusively with a Rhizopogon species complex (Rhizopogonaceae); pine drops (Pterospora) with two Rhizopogon species complexes; Sierra sap (Pleuricospora) with Gautieria spp. (Gautieriaceae); the gnome plant (Hemitomes) with Thelephoraceae spp.; pine foot (Pityopus), pine sap (Monotropa hypopithys) and candy cane (Allotropa) with Tricholoma spp. (Tricholomataceae); and Monotropastrum and Indian pipe (Monotropa uniflora) with Russulaceae spp. We found evidence of phylogenetic tracking in at least three clades of monotrope sister species which specialize on closely related fungal species.
Key words: fungi, Monotropoideae, mycorrhizae, non-photosynthetic, specialization