Know this plant?

Hello Everyone,

I'm curious to know if anyone can help identify what seems to be a volunteer/stowaway plant growing on my moss in several places. At first I thought it was some growth structure of the moss as it appears to be attached--but it seems too distinctive and un-moss-like. Whatever it is, it's growing fast and popping up in several places.

The plants I've intentionally added to the tank are below. This doesn't look like any version of them to me.

Rotala rotundiifolia
Dwarf baby tears (Hemianthus callitrichoides)
Utricularia graminifolia
Flame moss
Peacock moss

Thanks!