If you have ever searched for mycoheterotrophic plants in rain forest, you may be familiar with this phenomenon:

Voyria truncata (blue) and Voyria aurantiaca (yellow) co-occurring in a rain forest in Colombia.

Once you find a species, more species can often be found in the direct surroundings. Many botanists who studied mycoheterotrophic plants noticed this. In his treatment of the Burmanniaceae Frederik Jonker (1938) wrote:

“It is striking that at a certain habitat often a number of species grow together, often too in company with Triuridaceae and saprophytic Gentianaceae or Polygalaceae, so that one sometimes meets in a herbarium with several saprophytic species under the same collector’s number”

“In the literature several cases of saprophytes growing together are described, see van der Pijl (1934). van der Pijl presumes that this is produced by the presence of a fungus. However it is not yet known if the endophyte of all these saprophytes is identical, it is quite likely that it is in every case a Phycomycete, probably belonging to the Peronosporaceae”

We now know that the plants Jonker mentions target Glomeromycotina (not ‘Glomeromycota’ anymore, see here). Also, research has suggested that co-existing mycoheterotrophs do not necessarily grow on the same fungus. And indeed, if the fungi are ‘food’ for the mycoheterotrophs, then having a diverse diet may help to avoid competition with other mycoheterotrophs, and promore co-existence. But if the diets of two plants are completely different, then it becomes unlikely that they co-occur. To test this hypothesis, PhD student Sofia Gomes and myself teamed with MIT professor Serguei Saavedra. Together, we explored the fungal interaction patterns of mycoheterotrophs from several sites in French Guiana and Brazil.

Our hypothesis on how plant co-existence may be influenced by mycorrhizal interactions.

And indeed, the results show that in communities of co-occurring mycoheterotrophic plant species, the diversity of their fungal ‘diet’ appears to increase proportionally to their overlap in fungal ‘diet’. These results indicate that fungus-plant interactions can be better explained by understanding plant–plant interactions generated by sharing resources or fungal hosts.

It remains to be tested whether this symmetry between diversity and overlap in fungal diet may respond to an ecological mechanism driven by maximizing co-occurrence and avoiding competitive exclusion among mycoheterotrophic plants. However, the results show that plant coexistence cannot be fully understood without attention to their underground interactions.

The paper can be found here (open access): http://onlinelibrary.wiley.com/doi/10.1002/ece3.2974/full