The Crepidomanes and Hymenophyllum, as of December 2017, have been submersed for about 3 months, as best I can recall. The Trichomanes has been submersed about 3 weeks. All of them are doing superbly, with healthy and strong rhizome and foliage growth. I am loving how green and fresh they look.
Submersed Hymenophyllum species filmy fern
The aquatic growth is morphologically similar to terrestrial growth, but there are slight differences. The underwater fronds tend to look more basic or “immature” and are also much more translucent than terrestrial ones, and the rhizomes look more shaggy. The newer, submersed growth can be seen in the photos as being very bright, lime green, and as bushy rhizomes with orange-ish hairs.
Close up of submersed Hymenophyllum, showing fresh frond and rhizome growth
In the photos, any fronds that are darker green or have brown or black patches, are terrestrial growth from before the submersion experiment. In fact, the deterioration is preexisting, and doesn’t seem to be caused by being underwater. The healthy tissue of those leaves grown above water appears to be unaffected by being submersed for long periods of time (months) – if anything, it seems to rejuvenate them and make them look even better.