Central American ferns

Hi folks,

Am in Costa Rica for a couple weeks and have been trying to find resources on ferns of this region in English. There is Tropicos, but sifting through hundreds of species to try to find the right one is daunting, and there aren’t many confirmed observations in CR to go off of. I just need a foot in the door with more common species to get started. Ideas? Am willing to buy a book.


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Lellinger’s “The ferns and fern-allies of Costa Rica, Panama, and the Choco” (Pteridologia 2A) is at https://www.biodiversitylibrary.org/bibliography/124533 but is also available in print from the American Fern Society at https://www.amerfernsoc.org/pteridologia

Sadly, Part 2B was never issued, so it is incomplete, but potentially allows species-level keying for what it does cover.

I can also recommend Lellinger’s multilingual glossary (Pteridologia 3; https://www.biodiversitylibrary.org/item/216418). It might help you with Flora Mesoamericana, which should have a complete (if slightly taxonomically dated) treatment of Central American ferns, and is available online (http://legacy.tropicos.org/Project/FM) but is written in Spanish.

I generally consider it a good day when I can get a Neotropical fern on iNaturalist down to genus, although some of my friends can regularly do better. It is often hard to pause and get good photos that show all the key characters for a given group. Most of the major families do have a pretty distinctive gestalt (e.g., the linear sori along veins of Asplenium, not paired as in Diplazium, the typical pinnatifid dissection of Blechnaceae, with linear sori and often dimorphic fronds, and so on) but one excellent trick when dealing with completely baffling material (if you can do it safely and with permission) is to pick a frond and see whether it has 2 vascular bundles in the petiole/leaf stalk/stipe or 2 + several smaller ones, which distinguishes between eupolypods II/Aspleniineae and eupolypods I/Polypodiineae. (Obviously there are ferns that are not eupolypods, but this covers a considerable amount of ground.) I will see if I can think of any other good high-value things to photograph for distinctive groups.

It’s hard to pick a common species because there are so many! Christella dentata is a rather fuzzy, alien fern which is widespread, particularly in somewhat disturbed areas. Pityrogrammas are lacy with colored farina beneath and also tend to show up in somewhat disturbed places and canopy gaps. For tree ferns, if you can get a frond, you need to look at the scales on the petiole (of the frond); an apical bristle on the scale distinguishes between Cyathea and Alsophila. For filmy ferns, try to find fertile material; usually Hymenophyllum has clamshell-shaped indusia and the trichomanoids have a cuplike indusium with projecting bristle bearing sporangia. There is lots of Nephrolepis; when the fronds are in decent condition, the tip is coiled up like a tiny fiddlehead. There are one zillion species of Elaphoglossum, which are fairly common; for that genus and Pleopeltis, macro closeups of the scales are super helpful.

Hope this gives you at least something to start thinking about. I spent a week in Costa Rica last year with the OTS Ferns & Lycophytes class, and it was extremely instructive and a most enjoyable experience. Don’t step on a terciopelo.



Thank you, Chris—very instructive post. ID’ing ferns in the tropics, as I’m learning, and as your post elucidates, is very daunting. 800 or so species in this country alone! I went on a hike today and I swear I saw a hundred different looking ferns—plastered on and hanging from every surface available. Thank you for the advice on starting with Genus first. Will give that a go and check out the resources you posted.

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Oh one more thing, have you heard of any ferns that would be unsafe (for the human) to touch? I’m very careful about touching leaves in the jungle that I know nothing about.

I don’t know of any ferns that reliably generate dermatitis in the way that, say, poison ivy does, and that’s a sufficiently weird and alarming feature that I think I would be aware of it. Supposedly some people find the fine hairs from tree ferns irritating, but they’re not “stinging” the way nettles are.

That said, situational awareness is always good in the tropics: you should be looking to make sure you’re not grabbing a bullet ant or an eyelash viper with whatever you did intend to touch. If the canopy gives you Microgramma brunei, a cute little entire-leaved polypod with a bunch of mysterious potato-like structures attached (https://www.fernsoftheworld.com/2015/01/21/microgramma-brunei-werckle-ex-christ-lellinger/) politely decline the gift; the structures are domatia for a set of aggressive ants. (This is very unlikely to be an issue but it’s one of the few contact dangers I can think of directly associated with a fern as opposed to being careful about thorns and venomous things in general in the jungle.)


Latitudinal biodiversity gradient strikes again! The fern flora of, say, eastern North America (let’s exclude Florida for the moment) is sufficiently small that it’s not hard to eventually be able to site-recognize every species, excepting a few intransigent cases like Polypodium. As you can see, that’s a lot more difficult in the tropics because the flora is so explosively rich.

If you have fresh material on hand, and especially if you can use the vascular bundle trick and soral appearance/placement to help with some of the more nondescript-looking specimens, it’s usually possible to get material to genus. People with experience of a particular group or area will often be able to go “oh, yeah, that’s species X, there’s nothing else like it here” but those of us more bound to keys will generally not have time to key material to species in the field.


I have been tagging you on Pre-Maverick ferns in Africa. Thank you for your help.

Pre-Maverick ferns in Costa Rica 32 obs - I wonder if it is possible to resolve some of them? Or if that would make a good first lesson?

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