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There’s a lot of green in the world, and that is thanks in no small part
to the microcosmos. Not only did cyanobacteria lay the foundation for an oxygenated Earth,
they laid the foundation for chloroplasts when they were endosymbiotically consumed helping
their host take on their photosynthetic machinery. For most of us, the green we are confronted with
every day is a more macroscopic kind, the leaves you see on trees and grass. And if you’re on a
hike, you might notice some squishy bundles of green flush against a tree, or low to the ground.
“Oh, a moss,” you might tell yourself. Or “oh, a lichen!” And then, perhaps, you move on, unsure
of whether you’ve called it the right thing but distracted by the many other sights around you.
But today we’re not going to let that happen. We’re going to linger
on our non-vascular plant friends and look at them a little closer,
learning more about what they are, and why only one of those things is actually a plant.
…it’s the moss. Moss is the plant. More specifically, moss is a member of the
plant division called Bryophyta. And when we say that moss is a non-vascular plant, what we mean
is that it doesn’t have the vascular tissue like a xylem and phloem to transport water and nutrients
around the plant. This lack of vasculature keeps mosses short so that they can still transport
nutrients and water easily. And while they don’t technically have roots or leaves as defined for
vascular plants, you’ll see the equivalent structures like their root-like filaments
called rhizoids and also these leafy parts. And mosses provide a lot of benefits to the
environment around them. They help prevent erosion, and they can provide insulation.
And we’ve seen ourselves how mosses provide a home to some of our favorite microbial companions.
Lichen on the other hand though they are sometimes called non-vascular plants,
they are very definitely not plants. So what is lichen?
In a 2010 Discovery article, the lichenologist Trevor Goward described lichen as “fungi
that have discovered agriculture.” To be more specific,
lichen is a symbiotic union between a fungus and an algae. The fungus provides access to nutrients,
as well as protection from the elements and UV light. And in exchange, the algae
provides its own photosynthetic capabilities. Now that sounds straightforward enough, especially
when you consider all the symbiotic relationships we’ve learned about in the microcosmos.
Put together the right fungus, and the right algae, and you get a lichen…right?
Well, scientists have attempted to create lichens in the lab by culturing
the appropriate partners together, but with little success. And it turns out
that that might be because we’ve underestimated the number of partners involved. In one study,
scientists found that there was at least one other fungal partner in their lichens.
And it could be that other species have many many other members involved, making them
far more complex than we have understood thus far. For something so strange and complicated,
lichens are amazingly prevalent: they’re estimated to cover up to around 6% of our planet’s surface,
whether that’s on the side of a tree or on a rock or even on dunes. And lichens have this ability
to not only latch on to all sorts of surfaces, but to disrupt them and convert them into a more
habitable environment by releasing minerals and creating the early ingredients for future soil.
And so because lichens are so important to cultivating the seemingly inhospitable parts of
our world, many have thought lichens were possibly one of the first organisms to make it onto land.
But research from 2019 has suggested that lichens didn’t find their way to land until well after
vascular plants did. In fact, it could be as long as 100 million years after, raising new questions
about how plants and our own earth evolved. Now mosses are also part of this story,
as they were likely among the earliest plants to make it onto land. And their ancient spread may
have played an important role in raising oxygen levels to where they are today,
allowing for the evolution of not just other plant life, but of more complex animal bodies as well.
With that said, the trick with evolution is to know that creating a whole world
is much more complicated than any one step would have you believe. Mosses and
lichens carry their own worlds in their spreading masses, not fully invisible like the microcosmos,
but often underfoot and easy to ignore. But maybe if you spot some on a walk, take a moment
to look a little closer, and to wonder what other secrets they might possibly hide.
Thank you for coming on this journey with us as we explore the unseen world that surrounds us.
And thank you again to Skillshare for supporting this video.
After staring at all of this moss, maybe you’re thinking, “You know,
I could use more plants around the house.” But you might also be worried that you don’t have the
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