Well, aside from compulsive plant collecting, and my collection of musical instruments (my interests, of course)....
I have a collection of odd hats::
cowboy hat
railroad conductor's hat
furry Russian hat
wizard hat
French Foreign Legion hat
camouflage fisherman's hat
huge straw hat
ski hat
There are probably some more I am forgetting.
I have no idea why I've collected odd hats. I actually hate wearing hats for very long.
Wait, maybe I do have an idea why...
It probably has to do with the historical-sociological context of most of these hats...
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Plantae/Magnoliophyta/Magnoliopsida/Fabales/Fabaceae/Mimosoideae/Acacia