It's probably perlite, little bits of volcanic glass used to help prevent soil compaction. This stuff is an impaction risk to your frogs and make absolutely sure that you remove all of it before putting the plant in your vivarium. I just rinse the potting soil off, rinse the plant, and triple check that no perlite is still attached to the plant before using in a vivarium.
I've only been to a handful of reptile expos, but I've found much better deals on plants elsewhere. It's a good place to go for ideas though, you'll hopefully find a few planted tanks on display.
It could be that it will never cause problems for frogs, I don't really care for the plant in any case so I don't bother with it.





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