20-day timelapse of iridescent thing (June 4 to 24)

 

Note the stick in the top left. I painstakingly adjusted both pics so the stick was pretty much the same angle and size in each. I also no longer think there is much chance of it being a marchantiophyte; morphological cues strongly hint to me it is a self-replicating fern gametophyte that is unable or unwilling to produce sporophytes.

Also, I am planning to send it to a lab for analysis! To my (and the fern researcher I talked to's) knowledge, iridescence has never been documented in fern gametophytes before.