Moss. A colony I've been monitoring for several weeks. I believe that it is either Gigaspermum repens or Goniomitrium acuminatum, but do not know enough to opt for either. What is on CNP as G. repens appears to be a mixture of both species.
20 July added 4th image (taken that day), enlargement of part of same specimen. My interpretation (possibly wrong) is that the foliar part of the sporophyte falls off (looking like a dunce's cap in the photo) leaving an open cup from which spore is released.