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Rhizopogon is a genus of hypogeous (underground) Basidiomycetes. Recent micromorphological and molecular phylogenetic study has established that Rhizopogon is a member of the Boletales, closely related to Suillus. All species of Rhizopogon are ectomycorrhizal and are thought to play an important role in the ecology of coniferous forests. R. luteolus was deliberately introduced into Pinus radiata plantations in Western Australia to improve tree growth in the early part of the 20th century.
Orchid mycorrhiza in Rhizopogon are suspected of having a treesome-relationship: the fungus is ectomycorrhizal on the roots of coniforous trees and shrubs on one side, and forms orchid mycorrhiza on the other side. This makes it difficult to continue orchid cultivation after the protocorm stage: the fungus will require a marriage with a tree or shrub to maintain the orchid. Typically the orchids associated with Rhizopogon are aclorophyllous and don't survive transplantation because the link to the tree is broken.
Rhizopogon vinicolor A.H. Sm.
Daniel B. Wheeler wrote:
"While a student at Oregon State University, I was informed that Helen Gilkey had cultivated several species of Corallorhiza[sic] (sp?) orchids by first growing Rhizopogon vinicolor (a very common hypogeous fungi which the orchids live off of) first in association with Douglas-fir seedlings. She was the only preson I know of who has been successful at such cultivation.
It is illegal in California and Oregon to possess even a single flower of these orchids. The fine, as I recall, used to be $500 per flower, and a single stem of these orchids may have 40-200 flowers/buds/seed pods on it. So possession of a stem if you are caught could net you a rather hefty fine. OTOH, very few people know these are orchids anyway…
Rhizopogon vinicolor is relatively easy to introduce to Douglas-fir. A simple slurry of sporocarps sprayed 2-4 times on seedling trees will ensure nearly 95% colonization of the rootlets if done during the spring. Each slurry application should be done after 2-3 weeks intervals, and preferably during a rain so spores can be washed into the soil near the seedling tree rootlets. Spores not in close proximity to rootlets do not appear to germinate.
Since R. vinicolor is mostly spores, a single average sporocarp of 1 inch diameter will inoculate around a million seedling trees, or enough to reforest several square miles at 700 trees per acre. " 1)