This spontaneously generated in some potting soil that also grew moss. It appeared after some compostable seed starting pots were left in moist zip-loc bags for the better part of a year. Any idea??? It likes a very wet soil and low air flow (apparently) and is about the size of my little fingertip:
There is another picture, from top view showing the leaf more clearly, here. Thanks in advance if any ideas! Unfortunately I may have killed this trying to move it into its own pot, but we'll see. The hairs were very sticky and immediately got gunked up with potting soil when moved.