Did you have moss there to begin with? Are you growing these in a container in sterile soil? If so, I think it is unlikely to be moss as where would the moss spores have come from?

Spores are everywhere. I often have moss volunteer in fern sowings, even if I've sterilized the soil--all it takes is opening the lid a couple of times and if there's moss around a few airborne spores can get in. Anyways... for the original question... very young fern gametophytes can't really be distinguished from really young moss gametophytes without some high magnifications and whatnot. Once they're large enough to look like dots, though, you can be pretty sure they're ferns. Mosses will either have distinguishable "leaves" or no distinguishable form at all, consisting merely of single cell thick threads before they produce anything larger and more exciting. It's also common for fern gametophytes to be fairly irregular, rather than the nice flat heart-shaped guys that make for better pictures.

Patrick Alexander

A little update on my window's Polypodium aureum culture. One week ago (about two months after sowing spores) most of the previously spongy-looking clumps of green cells turned into heart-shaped prothalii. No moss on sight up to now. However, some mould have developed. It seems not to affect the prothalii seriously, but I'll keep one eye on it. Prothalii are now about 1.5-2 mm across, looking flat and darker towards the "lobes" of the heart, and paler, brighter and with a "hairy?" surface towards the tip. I'll let you all know when they develope into something else.

It's been a long time since last post, and I decided to write a follow up. I hope this info will help other people, as I would have benefited from it if it was available one year ago.

At today, some 8 months after spores sawing, this is the state of the culture:

Prothalii are now between 5 and 10 mm. across, much bigger in one container than in the other, I guess due to difference in moisture or sawing density (more sparse in the container with bigger prothalii).

About 3 months after the prothalii adopted their heart-shape, one or two on each container (2 Philadelphia creem cheese containers, those flat ones of salmon flavored cheese), decided to start their tinny ferns, which are on a 3-leaves state now (each about 0.3" long).

My containers are on ziplock bags as to keep the moisture, with a few millimeters of water inside the bag (but as the containers are not perforated, they do not get soaked inside). However, it seems that the architecture of the ensamble allowed the water from the substrate to vaporize, then condensate on the sides of the bag, and finally drain throug the bag to the bottom, the result being a pot with dry substrate and a green venier of prothalii floating on half an inch of water.

I figured out that it was not good for those guys, as masculine gametes need water to swim and then reach feminin gametes (which are immobile). Then, I vaporized with water the surface of the culture a couple of times, spaced about 5 days. That seems to have been very appropriate, as two weeks after that there are countless prothalii starting to produce young ferns.

I'm currently keeping an eye on them as to avoid new droughts, even if the relative humidity keeps always elevated inside the bags.

I'll update this when something else happens.