Why are bryophytes always left out of plant discussion?

Nature Talk
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I have seen many papers about plant biodiversity (past and present), biogeography, macroecology, and conservation. For some reason, they almost always only talk about “vascular plants” but never simply “plants”. Why is that? What are mosses, liverworts, and hornworts put on the wayside?

They are never taken into account when making phytogeographic realms/provinces, as far as I’ve seen. And macroecological studies that study many plant species in a global/holistic manner also tend to focus only on vascular plants. And studies about diversification of plants across geologic time also are mostly limited to vascular plants. So what is the deal here?

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two reasons:

  • they are much harder to Identify, less people work (and worked) with them, so our current knowledge of distribution is less reliably complete, esp. outside Europa and N. America. The scant historical record also means it is hard to identifiy non- native mosses (there are quite a few mosses that are very rare in europe, but very common in eastern N. America, there are several mechanisms that could explain this pattern, one of which is that (at least for some of) those mosses are not native to Europe)

  • at the scales you are mentioning they do not behave like vascular plants; I think they would actually need their own phytogeographic realms and provinces. mosses are more prone to being cosmopolitan or have really wide distributions, endemics are few; their are much mor eprone to lingering in areas they should not, because they found a patch of suitable microenvironment.
    I work across a boundary between (sub)mediterranean and temperate Europe, and while the vascular plant show a strong signal in this climatic boundary, the mosses do not yet, for them the climatic boundary is much more to the south . to mosses both areas look similar, they can grow a similar ammount of days in both areas; and the difference in frost severity and summer drought duration are not yet enough to make a big difference.

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And yet it would be interesting and instructive to compare these with those of vascular plants.

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Thank you. I was just gonna say that.
You explained perfectly.
Respect to bro because he knows what he’s talking about.

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It is true that mosses work differently than vascular plants, but can one also not make the argument that vascular plants are extremely diverse among themselves? Every species has its own particular range of humidity tolerance, thermal tolerance, relationship with animals, etc. The whole point of such maps is to get a big aggregate picture, and I don’t see why bryophytes should be excluded from that.

And if I may ask, what makes bryophytes much harder to identify than vascular plants?

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Most of them require microscopy work to ID at all, and there is also a severe shortage of decent field guides or keys. Most papers about them are very technical and hard to decipher by non-experts, and locked behind paywalls to boot.

At least that’s been my experience - I set out to learn my local mosses and liverworts with great enthusiasm, and eventually had to give up.

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It is true that mosses work differently than vascular plants, but can one also not make the argument that vascular plants are extremely diverse among themselves?

One could; and it is not entirely wrong.

However, usually, in vascular plants, there are detectable and repeating patterns in many groups that are smiliar enough; and enable us to detect and analyse such patterns (e. g. Cardamine kitaibelii, Ostrya carpinifolia, Epimedium alpinum, Campanula pyramidalis, Helleborus niger, Omphalodes verna etc. all have distributions centered in NE Adriatic; probably because there was a glacial refugium somewhere in W Slovenia/NW Croatia/NE Italy). These patterns are called chorotypes, and usually it is not difficult to assign them to plant species (chorotypes can overlap, the chorotype in the upper example is Illyrian; but some species (Cardamine and Ostrya) are actually Amphiadriatic)

Such patterns of centered distribution and endemism to certain areas fo the world are common and predictable in vascular plants (there is little debate on how/where to make phytogeographical divisions; more how exactly to group the together and their hierarchy). If you click through plants with a lot of observations in Europe you will notice patterns.

In mosses these patterns are less clear and more blurry, because mosses usually have quite a broad distribution, and are less bound by dispersion difficulties; and most importantly, the drivers for the distribution patterns are different for mosses than for vascular plants.
There are some phytogeographic concepts for mosses (i.e. hyperoceanic); but I do not think there is a thourough sisytem(s) as there are for plants.

TLDR:

Vascular plants are more likely to repeat distribution patterens across unrelated taxa, and are mostly dependent on similar drivers across taxa; vascular plants and mosses have different drivers for their distribution patterns, and I think it would not make sense to mix them.

And if I may ask, what makes bryophytes much harder to identify than vascular plants?

I can only assume you did not try to ID a moss before? If I am correct, I encourage you to try; the question will anwer itself :D

Working with vascular plants, you can walk along a trail and make good surveys, only needing to take home maybe the difficult grass or couple of the apomictic genera (if you even care about apomicts - I personally do not). And even then, usually a stereomicroscope is enough, and only rarely you need to make dissections and crosssections to meake a good ID you are sure of.
I would go and say that perhaps making vascular plant survey is the easiest type of survey to make - they are always there, do not run away, and vast majority of them can be determined just by looking at them with your eyes and a loupe.

For mosses, at least 50% of the species is not determinable with 100% certainty in the field.
Then, you need a microscope and many species need thorough dissesction, and making of crosssections, and the absolute winner - looking for sexual organs, as often the only sure difference beteen species is their sexuality etc.
And even then, If you have infertile material, it may be impossible to make ID. It takes more time than making plant surveys, and it’s difficult.

I would say it is not harder than making thorough invertebrate surveys, but can approach it in some ways.

And 50% is for bryologists with some experience. If you include a thorough knowledge of their local ecology, it can be more if you really know what you are doing.

TLDR:
Basically, mosses are harder to ID, because they are small, and you need a microscope to see diagnostic features, and only some of them are distictive enough to make a confident ID in the field.

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Hmm. I thought that mosses, being much more dessication sensitive than vascular plants, would actually have more restricted and endemic distributions than vascular plants. Because seeds are truly hardly little guys, they can be transported across wind, oceans and migrating animals and stay dormant but viable for decades until sprouting. This is a generalization, but generally wouldnt the propagules of vascular plants be better dispersers than those of bryophytes?

As for the id stuff, it sounds a lot like the difference between vertebrates and arthropods (and probbaly most other non vertebrates)…

(Also I assume everything you said about mosses is applicable to hornworts and liverworts too?)

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moss spores are tiny, and also quite hardy and can be dispersed by wind very far. Many mosses are also dispersed by gemmae (non- sexual propagules, usually some form of a bunch of cells, capable of makinga whole plant)

Plant seeds are mostly large and heavy, and even those with special adaptation are not usually actually dispersed that far (not more than 5 km), the exception being zoochoric species (there are documented cases of birds taking seeeds 1000s of km far, but tis is a big exception).

Rule of thumb; the smaller a propagule is, further it goes.

Mosses are far more dessciation tolerant than vascular plants, vast majority of them can survive complete dessication (there are two groups that do not, aquatic/wetland mosses, and hyperoceanic mosses).
There are differences in how often and for how long a moss species will tolerate dessication - species like Grimmia pulvinata (https://www.inaturalist.org/observations/106674108) can survive dessciation often and for long periods of time, and grow on dry limestone cliffs and walls also in mediterranean, where droughts are long and severe; others, like this Echinodium (https://www.inaturalist.org/observations/241267738) are so sensitive to dessication they only live on hyperoceanic islands, and even then in narrow gorges close to water ways.

Most fall in bethween and there is then a gradation of species from humid to dry air places.
but even in high rainfall places, mosses often dry out (imagine a moss growing on bark of a tree - even if it rains almost every day, the tree stem usually dries in between the rainfalls).
And overall, one of the factors determining which moss species will grow in a place is dependent on grwong days, i.e. days that are humid and warm enough for a moss to grow in that environment.

Yes, i use the word moss in its widest sense, including those two groups. hornworts are species poor, while liverworts are similar to mosses. In humid envronkment they are more prominent, in dry less; but even in driest places there will be a liverwort or two hiding somewhere.

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This is exactly right, i work in wetlands in the soggy northeastern United States and the same patterns hold true here.

Some mosses, like Sphagnums, can be important indicators of tiny scale conditions within a wetland. They do say a lot about moisture and temperature. But they are not good indicators for rapid assessments, with a few exceptions, because they are difficult to identify and taxonomically confusing. It doesn’t matter how important thye are, if you’ve got very limited time and resources you will look more at trees as indicators of ecological condition tan you will at mosses that need a microscope to identify.

And yes their ranges are very strange. The same as fungi and likely it’s because of the spores as noted above. This makes them less useful for defining ecoregions.

But yes they are very important and worthy of study, and just our size relative to them introduces bias that means we look at them less.

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So this begs the question. What do you think floristic regions based on bryophytes would look like? The few maps that do exist seem to suggest they are more diverse in higher than lower latitudes, and more in montane areas than lowlands. Weather this is sampling bias or represents a real trend I have no idea.

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Just adding that I profiled the top sphagnum identifier on iNat a few months ago, if you’re interested.

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no, that is probably a real trend, temperate montane areas are probably some of the richer areas.
Other areas where there is high diversity are tropical cloud forests, but these are less sampled and there is likely much undescribed (I m not sure if diversity there is greater though, although the conditions are good and there are more niches, there is more competition from vascular plants in roles they do not fill in temperate belt).

Western and central Europa are decently sampled, and here the richest areas are (Hyper)oceanic Europe (particularly Western Scotland and Norway, but aso other oceanic regions), Macaronesia, and the wet mountains (Southern Alps, Dinarides, sections of Carpathians).

Per surface area, Slovenia is probably the richest in bryophytes (800+), other centres are Scotland (1000+) and Austria (1000+), the whole Europe ~ 1900.
The country with most species of bryophytes in Europe is porbably Italy (1200+) which spans almost the whole span of climatic conditions in Europe (tundra in the alps to mediterranean desert in Sicily).

I am not sure exactly how the map would look like; in Europe we would probably have 4 provinces; hyperoceanic, nemoral (oceanic/subpoceanic) mediterranean and boreal.

Nemoral and boreal belt if Europe would probably like in vascular plants continue eastwards into Siberia and N. America; where I am pretty sure again you would have a hyperoceanic province/kingdom in PNW and western Canada (to which pacific island may also belong), and a mediterranean in California. Also pretty sure USA South would be something at some level.

For equatorial region and souther hemisphere I do not wish to even hazard a guess.

the biggest difference would be the existence of Hyperoceanic belts (which might belong to tropical kingdoms, or form a specieal kingdom togther with cloud forests of tropics; there are conections, like Jubula, Southbyaceae and Dumortiera, Lejeuneaceae etc.) and that mediterranean provinces would be significantly smaller.

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If i may ask, what exactly does hyperoceanic mean?

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oceanic in terms of climate means a climate significantly influenced by oceans in the way of reducing temperature extremes, increasing humidity and icnreasing frequency (but not necessarily ammount) of percipitation.

hyperoceanic is used when all this happens at the extreme, and usually where there is a mountain range limiting airflow between the oceanic side and continental side (e. g. Scotland, Norway, Northern Spain, Pacific North west of north America, Southern Chile and New Zealand), increasing the percipitation, reducing bursts of cold and dry air from the continent in the winter etc.

hyperoceanic basically means oceanic with little to no infulence of the continent (difference in climate between northwestern Scotland and London, both are gray and damp, but one is significantly more so)

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