the identity of the mycorrhizal symbiont of an orchid species is evidence
for its taxonomic position within
Orchidaceae.

Funny that Robert Dressler, the doyen of orchid taxonomy, has never even
mentioned it. What scientific studies or evidence do you have to back this up?
Can you give a specific example?
Iris,
Central NY, Zone 5a, Sunset Zone 40
"If we see light at the end of the tunnel, It's the light of the oncoming
train."
Robert Lowell (1917-1977)