I put the question whether mycorrhizal associations are useful in
orchid systematics to the systematists on the discussion group TAXACOM
and received this answer:

"I have just attended the Species Plantarum 250 symposium in UPPSala.
The last speaker from Germany or Austria gave his entire talk on the
significance of mycorrhiza to plant taxonomy. Please contact Magnus
Popp at Uppsala Sweden to get the details of this person."

I have contacted Magnus Popp and will let this group know if anything
regarding the Orchidaceae comes to light.

Someone else volunteered "Tupac Otero and Mark Clements here at the
Centre for Plant Biodiversity Researchand the Australian National
Herbarium are looking at this issue in Australian Orchidaceae using a
range of molecular techniques, and Tupac has done similar research in
the neotropics."

They are apparently heading into the field, so I may contact them in a
couple of weeks.

Other posters mentioned host specificity in mycorrhizal associations
in the Ericaceae and Monotropaceae, so perhaps the idea is not as
far-fetched as it may sound.

Monique Reed