Thank you for your post. Good topic. The alternation of generations is a complicated process to understand.
Take a look at this image. I took this picture at Legoland, of all places, in California. I have never seen this before. Usually the sori are in the same stage of development, but I think in this photo, they are in many phases. You can see the beginning of the indusia on some of the sori. I think that it looks like they have a little piece of orange cloth in the center of them. But then what about the black sori? I have never seen that and I can not find a similar picture on the Internet. I assume that is mature indusia but whatever is on these black sori looks like a film of translucent rice paper. That seems like it would prevent wind dispersal.
Now, back to the fact that these were at Legoland, which has beautiful landscaping, I must admit. I am guessing that this plant is all jacked up on nutrients. Like this is a fern on steroids. If the nutrient supply is continuous, it might make the fern continue to produce sori before the older ones are dispersed, ie the nutrition might confuse the seasonal signaling.
If anyone can help me figure this out, I would appreciate it!
here is super close up:
Now I just don’t know what’s going on with the black sori at the top of the second image. That doesn’t look like a more mature indusia, mainly because the indusia are orange and that is some kind of translucent sheath. However, in the absence of some other explanation, that’s what I hypothesize.
Let me know what you think.