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@BrazenlyLiberal
Looks like one of these
https://www.mushroomexpert.com/coprinoid.html
Maybe this one
https://www.mushroomexpert.com/parasola_plicatilis.html
but one of the defining features of the family is the gills liquefy letting the cap curl up as the spores release, so identification is a moving target.
@AlphaCentauri
Thank you! I bet you're right. This one has been sitting out on the deck for not too long and the inky bits are more noticeable. It's hard to see in this picture, but liquid drops had appeared on it, too