what is the brown velvety coating on the underside of my staghorn leaves?

Question

Could this be fast growing and just appeared or more likely been there but not noticed?

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Answer 1

Staghorns produce Spores, not unlike mushrooms, as do all ferns. This is what you are seeing. Sometimes they will propagate if the environment is right.

This article will give you more information on the care of these plants: https://www.gardeningknowhow.com/ornamental/foliage/staghorn-fern/staghorn-fern-information.htm