How to organize foliage?

How to organize foliage?
What am I missing here?

You don’t.
However the search works if you know the names, and you can move the panel to a different monitor to help with the selection.
When you are working with assets which are not your own you are bound to not really know their name.
That’s about it.

Given Fortnight has maybe what 10 grass types? I doubt they’ll be updating the tool to handle categories (not that it wouldn’t be nice).

Try the Procedural Instance way if you don’t want to have to deal with managing the species.