I'm no genius when it comes to Polyrrhiza, (because I've never grown them). I have grown and am currently growing Chiloschistas. While they are difficult to grow for someone who's just starting out in the hobby. They haven't given me problems yet... Chiloschistas are probably the better choice for those who are starting out with growing leafless orchids.
Anyways...
These are my observations of Polyrrhiza from what I've seen in the pics posted here by mikeurquia, prem, and flhiker.
1. They're not twig epiphytes. They grow on medium to large exposed branches and lower to mid level medium to small sized tree trunks sometimes amongst very light patches of moss.
2. They're found mostly in the Florida Fakahatchee swamp forests. So research on this area of the US may be a good start. You also have flhiker, prem, and mikeurquia as resources, they hike through the areas where they grow in nature. Maybe they can give you an idea of what to do with them.
Here's what to look for:
a. temperature differences between night and day
b. temperature differences between seasons
c. during what part of the year does the area receive the highest average annual rainfall (also the least)
d. are there seasonal changes at all?
e. air circulation (this is where asking people like mikeurquia, prem, and flhiker come into play)
f. relative humidity
3. I recommend perusing the pictures that flhiker, prem, and mikeurquia have posted on the OB and really pay attention to the minutia.
Here're the links to their postings:
http://www.orchidboard.com/community...wers-once.html
http://www.orchidboard.com/community...st-orchid.html
http://www.orchidboard.com/community...-seed-pod.html
4. Mycorrhizal fungi plays a role in any orchid's success, but I'm not certain to what degree Polyrrhiza depends on them.
5. I believe lighting should be bright shade or dappled indirect light.
These are my
.