Distribution of Lichen-Species

Many of the most common lichens I find here in Europe seem to have a very large area of distribution. Most are at least holarctic, many are also present in other places. Here is a table of the 15 species of lichens (for simplicity only Lecanoromycetes) observed most often in Europe, their distribution, and their statuses according to iNat:

Species Distribution Status (Europe) Status (N.-America) Status (New Zealand)
Xanthoria parietina temperate native native native
Parmelia sulcata holarctic + NZ + AU native native —
Evernia prunastri holarctic native native not present
Hypogymnia physodes holarctic + NZ + AU — native —
Physcia adscendens temperate native native native
Protoparmeliopsis muralis mostly holarctic — native ?
Flavoparmelia caperata global native native —
Phlyctis argena global native — —
Cladonia fimbriata temperate native native native
Pseudevernia furfuracea holarctic — — not present
Ramalina farinacea mostly holarctic native native —
Lecidella elaeochroma holarctic + NZ + ZA native native —
Phaeophyscia orbicularis holarctic + NZ native native —
Lobaria pulmonaria temperate – South America — native ?
Peltigera praetextata holarctic — native ?

My first guess was that lichens (or their diaspores) are simply very likely to be hitchhikers on plants (especially because many of the above are epiphytes). However, that does not seem to be the case, judging at least by the fact that many are labeled “native” in both North America and Europe, some even in New Zealand. And in any case, I know that lichens are extremely sensitive to their environment, so it seems like all of them getting established in all these other places is unlikely, maybe?

My second guess is that most of these species of lichen must be very old. Assuming, the statuses are applied correctly, and these species haven’t therefore been distributed through human activity, these lichens must date back to when all the landmasses were connected, right?

What are your thoughts on this? :)


Notes on the table:

  • “temperate” has been simplified here to mean present on both hemispheres, with a gap in the middle (usually in the tropics)
  • “mostly holarctic” means there is a noticeable number of records in other places, but very dispersed
  • “—” means no status was applied
  • “?” means fewer than 5 observations in New Zealand
  • X. parietina is interestingly labeled introduced in Australia, which kinda makes me question whether it really is native to New Zealand
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Maybe it’s just that the splitters have been so busy making sure that no mushroom species occurs on more than one continent that they haven’t gotten around to doing the same for lichens yet.

I would think the reason these are the most observed is actually because they are very widely distributed. A species which is native to a small area would have only very few observations. I would think that includes a majority of lichen, but I could be wrong - I definitely have seen some lichen endemic to just a single small place.

And then what really makes lichen special is, most of them are restricted to pollution-free areas. And so they naturally only occur in areas with few people, away from polluted cities and agriculture. And that also means, away from potential observers. The 15 species above are mostly atypical ones which are tolerant to pollution - except maybe Lobaria pulmonaria, but that one just is really showy!

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True, but I only looked at the top observed in Europe, so how often they are seen somewhere else shouldn’t matter.
And that doesn’t explain how a lichen came to be native in Europe, North America, and New Zealand all at once.

They have to have made it across the ocean somehow or these species already existed before the current geography (but at those time scales and with the time they’d have spent physically separated in that case, that much similarity and there not being a speciation event seems almost impossible).

I’m assuming this is meant mostly jokingly, but I did think of the possibility of the lichens not actually being the same species (though again, the similarity seems far too strong for that level of isolation from each other).

In the fungal world, many species currently thought to be globally distributed are being split into American and European species. See Amanita pantherina and Amanita pantheroides, for example. I wouldn’t be surprised if we saw this in lichens as well.

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Spores are also much lighter than than plant seeds, so many fungi are able to travel further, unrelated but many bryophytes/ferns have ranges based on wind currents.

Specieation isn’t mandatory after a certain amount of time apart, some taxa are just really stable bc they just work.

I thought I knew the answers to your questions, but I found myself saying bc of the way it is, so I did some reading and research

I think these should answer a lot of your questions:

Especially this one: Biogeography and phylogeography of lichen fungi and their photobionts,
from Chapter 10 of Biogeography of Microscopic Organisms: Is Everything Small Everywhere?
- shared from my google drive starts on page 191

Past, present, and future research in bipolar lichen-forming fungi and their photobionts

Do lichens show latitudinal patterns of diversity?

Disjunctive distributions in the lichen-forming fungi

Uncharted terrain: the phylogeography of arctic and boreal lichens

Biogeography and ecology of Cetraria aculeata, a widely distributed lichen with a bipolar distribution

Low genetic diversity in Antarctic populations of the lichen-forming ascomycete Cetraria aculeata and its photobiont

Discovery of long-distance gamete dispersal in a lichen-forming ascomycete

Studies on the dispersal of lichen soredia

Aerial dispersal of lichen soredia in the maritime Antarctic

Understanding disjunct distribution patterns in lichenforming fungi: insights from Parmelina

Multiple, Distinct Intercontinental Lineages but Isolation of Australian Populations in a Cosmopolitan Lichen-Forming Fungal Taxon, Psora decipiens

After looking at these if there are still any questions on your mind, let me know

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Science has no universally applicable standard for how to delineate species, and (as has been discussed on this forum several times, including here: https://forum.inaturalist.org/t/why-do-some-genera-have-so-many-species/18452 ) is unlikely to ever do so. A species is functionally “A group of related organisms considered (in publication) by a taxonomist of that group to be a species, using whatever standard or definition that taxonomist preferred at the moment the analysis was performed.”
This being unfortunately true, discussions about distributions of species are extremely prone to being mostly semantics.

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Looking at the papers above, I think for this specific questions the species delineation is not that relevant since “genetic distance” of sampled lichen can be measured, to infer things like dispersal patterns. With limitations of course, but the currently assigned name or species rank doesn’t seem to matter for the results.

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I’ve started reading into these. They’re very informative! Thank you! :D

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but the specific question is “Distribution of Lichen-Species.” Species delineation is very relevant to that question. A taxonomist could easily (and some likely will at some point) decide that the New Zealand populations, the American populations, the populations in Europe, etc. are different sets of species, and that would very much affect the results of any species-based distribution analysis.
Many of the papers cited above ask a different question. Not why species are distributed as they are, but how genetic diversity is distributed. This is (in my view) a more productive way to ask the question because it does not depend on (necessarily arbitrary) species labels.

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So if eyekosaeder has their curiosity fulfilled regardless of semantics, why focus on the use of the term species?

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Because the question they are asking, and the data in their table, are about species. I’m glad that the papers you shared mostly don’t focus on species distributions, and I think it is worth making people aware of the difference in approach between species distributions and phylogeography.

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