I have a fern which I feel must be the kind you inquire about. My friend, who gave it to me several years ago when it was about to die, called it an alligator birdnest fern. Today I was checking to try to identify it more exactly, and your post came up.

Is this what you refer to?
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and it seems to me that it does multiply by clumping, because I am about to have a local nurseryman separate and repot it for me. I do not want to chance losing it now.
Actually, the long fronds are greater than 2 feet long.
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And while we are on the subject, I found a different style birdnest fern at the nursery I spoke of, sort of a clubfoot version, different from my other wavy edged and straight edged bird nest ferns. I am quite fond of these plants, and give them a place of respect in the limited shade of my garden.
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Hope this helps.

This one is about a meter in diameter. It lives in a large, glazed pot underneath one of my live oak trees. It gets dappled sunlight until later afternoon and then a bit of direct, but low, sun. I think I've had it ten years or more. It tolerates cold including freezing nights very well. When the temps are projected to go unusually low, I toss a sheet over it.

Carol in Jacksonville.

The "Crocodile Fern" is Microsorum musifolium and not related to the Birdsnest Ferns, Asplenium nidus/australasicum. They're not clumped like Birdsnests but have a running rhizome that the fronds come up from.