Do any Juncus have flowers that look like that? My first thought was a very small lily of some sort but I did I looked at photos of all the genera of Liliacaea in MO and none looked at all like this. I'm pretty stumped and of course I can't go back and see it again/try to key it out now.
It was at the edge of a calcareous fen and mesic woodland in Reynolds co Missouri. The ground was muddy and water was slowly seeping out of the ground, growing in the shade.
Looks rather like Eriogonum inflatum, but wrong location and that species has yellow flowers. Flora of Missouri only list two other eriogonums and they are not it.
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