Yes, the tiny 'clover-shaped' leaflets emerging from the prothalli patches are the first fronds of whatever fern species you've got in there. In a terrarium, ambient humidity alone is often sufficient for fertilisation to occur, but you can always help it along with extra misting. That's all that's required in most cases - only rarely do you need to resort literally to soaking a batch of reluctant prothalli.

Thanks! I'm so exited! This is a fern that I got this past May, and immediately put in my terrarium. I am thinking that I probably started seeing the first patches of prothalli by July or so.
I also have one more question. At what point should I pot up the baby ferns and start to acclimatize them to the outside world?
Thanks again,
-Jmcat

There isn't a definitive answer to this - it's up to you really. In theory, you can prick out sporelings at any stage - from early one-frond babies to much older multi-leaf specimens. But the growing-on time will need to be many months if you prick-out right away - you're looking at keeping any vulnerable new transplant in a totally humid propagator box or poly bag for maybe six months, depending on the species and on your propagating conditions. A larger transplant will be that much tougher and not take as long to harden-off.

Professional growers, who depend on huge volume, might prick out at two or three-frond stage - whereas a hobby propagator, who only needs one or two plants for their collection, is just as likely to leave the baby ferns in-situ until only the strongest few are left...and only then selecting a couple of sturdy winners to pot-up. It's certainly easier doing it like this, but maybe not quite as much fun as going for it immediately you spot a few first-fronders to play with.

Why not combine both approaches? Get a humid propagator box or poly bag ready, plus a warm and bright place for it, and prick out a couple of baby plants right now. But leave plenty of other single-fronders behind in the terrarium so that you can study their development.

Oh, and remember to sterilise any compost you use for potting up those fragile single-fronders in a sealed environment - you'll have problems otherwise.

Thanks for the info. However, I don't entirely agree with what I've always heard about needing to sterilize everything before starting ferns. I have several different kinds of moss in this same terrarium. One or two of the moss clumps are about one inch away from some of the prothalli patches, but I haven't had any problems with moss crowding out the prothalli. Also, the soil was not (successfully) sterilized before making the terrarium, and some of the lid is open (it's a ten gal. fish tank that came with pieces of the hood already punched out). Now, I don't know if this is just because of having lower humidity than you would normally have for starting ferns, or what. Either way, though, I'm not complaining about not having to do the extra work of sterilizing the soil.
I'll see if I can post pics of this fern later to see if you or anyone else can id it.
-Jmcat

It's not the moss that you need to worry about when pricking-out vulnerable single-frond sporelings - it's the Sciarid Flies, or Fungus Gnats as you call them. Their rapidly hatching wormlike lavae can chomp through a tiny root in no time. That's why I still have to sterilise at this stage.

When the baby ferns are a little bigger they lose their vulnerability - but to begin with, and sitting in that fresh moist compost, they are absolutely sitting targets!

Simply steam your compost pots in the microwave for three or four minutes - that will zap any dormant gnats' eggs. Cover and allow to cool and THEN prick-out.

Sorry for my ignorance on the subject, but I'm still not understanding why Fungus Gnats would be a problem after pricking out the young ones but not before.
Thanks,
-Jmcat

Why do you need to microwave your propagating medium? Because the rich, fresh and wet compost - unsterilised and sealed in a poly bag or propagator box - will be the ideal breeding ground for the Sciarid Flies whose eggs are likely to be in your proprietary compost. And there will now be nothing else in that confined environment to distract the lavae, just the sitting-duck of your one pricked-out sporeling.

Sciarid Fly is still a possibility in an established terrarium: but a mature system is altogether more balanced, the moisture is lower, the compost has lost lost much of its organic material, and anyway there is considerable safety in numbers for your zillions of prothalli. Not so in your poly bag!

It's not religious dogma or anything - just an insurance policy. When transplanting vulnerably slow developing single-frond ferns it's a false economy not to microwave for a few minutes.

Ok, I understand what you're saying now. Thanks for the clarification!
-Jmcat

Good info for jmcat, Stephen. A couple things I've used for the gnats is baccilus thurin..(sp) and the sticky yellow paper. I have also heard that if you capture a spider from your garden and put him into the spore bed with the gnat problem the spider will eat all the bugs and larvae then die.

I see that Imageshack has been fixed so that you can log in again, so now I can post pics of that fern.
Here is a close-up of the end of one of the uncurling fiddleheads:
{{gwi:617518}}

The previous pic had more accurate color balance, but here is the end of a mature leaf:
{{gwi:617519}}

And here are the beginnings of leaves on the prothalli. Again, these are the same color as the rest of the fern:
{{gwi:617521}}

The fern is approx. 3 inches tall,3 inches wide, and the leaves are about 3 1/2" long. When I found it, it was growing on a slight hill, partially under a rock, in fairly dry conditions (there were prickly pear and barrel cacti on the same hill).

When I was just looking at it to determine size, a few more questions came up. First, should I cut off the dead leaves (since I got it, it has had the old leaves die off and new leaves replace them)? Second, why on earth doesn't it have any spore cases on these leaves??? I was examining the leaves and saw that none of them have spore cases. When I first got this fern, I could easily see spore cases on the underside of the leaves, but now I can't, even on the fairly new leaves. Would this be because of the difference of climates between where it was and where it is now? Any ideas?
Thanks,
-Jmcat

Why ferns do and do not produce spores can be the subject of much discussion. One thing you will notice is that spore cases, when first forming can often be difficult to see. In the case of many ferns, spore may take a year to mature on the frond. I some cases it never properly matures and aborts or is simply non-viable. I presently am growing Cibotium schiedei which has produced spore cases for the past two years, yet the spore has failed to properly mature. Recently on the Big Island of Hawaii, I noted that, all things being equal, fronds produced in higher light levels, on the same plant, will produce more and better spores.

Thanks. My guess would be that the light level is causing the problem, then. This fern probably got plenty of light where it was, but I can easily tell that the light in this terrarium is not as good as the light in my other terr. right next to it. not only is this light not as bright, but it also has a very different color balance.
-Jmcat