That's interesting SOS! I'll have to look into that.
And I know that this is a pretty big generalization with orchids being so diverse, I was just wondering if there were ANY that were. I know how annoying broad statements can be.
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Sorry I didn't make it clearer.
It would make sense to me that epiphytes and plants like Spider plants that grow somewhat airborne (for lack of a better word...) would "use" (again, for lack of a better word) the air more? I can't find a better way to explain my thought process, hahaha! Thus, process more CO2 and filter more air in a day than a more terrestrial plant. I hope that kind of makes sense, I could be completely off track for all I know.