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Originally Posted by Raul-7
Does the Microsorum actually release viable meiospores from those sporangia, or is it in that state where it "thinks" it's growing terrestrially?
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I've tested sporangia from a submerged leaf under a microscope. The sporangium capsule functions in exactly the same manner like these of the most other so-named leptosporangiate ferns: remaining closed when wet, but ripping open and throwing the spores away when drying. M. pteropus is described as growing under water level fluctuations in their natural habitats (mainly streambanks). Therefore the spores are probably released only when the water level decreases.
EDIT: Sori on submerged M. pteropus seem to be common (but possibly not all variants of this species). Maybe this is an adaptation to fluctuating water level. The development of inflorescences by submerged Anubias seems to be a similar case.