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The first 100 people to click our description link will get a one week free trial. An ambiguously long time ago, there was this theory of medicine.

It was called the Doctrine of Signatures, and it persisted for centuries, maybe even millennia. The liverworts we’re looking at right now are a prime example of how this system conceptualized nature and medicine. The premise of the Doctrine of Signatures was so simple that honestly, we wish it were true.

The idea was that if you came across a plant that looked like a body part, that meant it was meant to treat ailments that targeted said part. In the 17th century, an English physician named Nicholas Culpepper said this of liverwort: It is a singular good Herb for all the diseases of the Liver, both to cool and cleanse it. All this pressure put on one tiny plant, simply because it resembled the liver.

Unfortunately, it turns out that medicine is a little more complicated than the Doctrine of Signatures. But even though liverworts cannot cure all the diseases of the liver, it’s still remarkably talented, capable of cloning itself in a series of steps that sound like they came right out of science fiction. To get a sense of what liverworts look like in nature, we can actually turn back to Nicholas Culpepper’s writing: "The Common Liverwort, groweth close and spreadeth much upon the ground in moyst and shadowy places, with many sad green leaves, or rather (as it were) sticking flat one to another, very unevenly cut in on the edges, and crumpled, from among which arise small slender stalks an Inch or two high at most, bearing small Starlike Flowers at the tops: The Roots are very fine and small."

The flowery structures and roots that Culpepper described might make you think that liverworts are just a normal plant. But liverworts are bryophytes— a loosely associated group of ancient but tiny plants that don’t have the vasculature we think of when we think of flowering plants. Without vascular structures like a xylem or phloem to transport nutrients and water around, bryophytes can’t grow quite as tall.

Instead, liverworts and their bryophyte compatriots, including mosses, tend to grow only a few centimeters tall. Even though they’re super low to the ground, liverworts make quite an impression. For one, they're bright green, filled with chlorophyll to help them perform photosynthesis.

But if you scan along the surface of some liverwort species, you might notice weird parts where the cells seem to warp and turn in a strange way, their insides filled with little discs made out of plant tissue. Why? We’ll get back to that in a bit.

There are two types of liverworts. The less common kind are called leafy liverworts because of their leafy scales and flat stems. These liverworts look a lot like moss, but their leafy structures are distinct enough that those who know what to look for can distinguish the two.

The other kind of liverworts are thalloid liverworts, which look more like scaly structures stretching out across the ground. When Culpepper described liverworts as having small, fine roots, he was almost correct. Liverworts do have small, hairy structures that help it latch onto surfaces.

These structures are called rhizoids, unlike roots, they aren’t able to absorb nutrients from their surroundings. These rhizoids are fascinating to look at because each one is a single cell, stretched out long and able to hold the liverwort in place. Another feature that distinguishes bryophytes like the liverwort from vascular plants is that they don’t reproduce with seeds.

Instead they rely on spores for sexual reproduction. To make this happen, liverworts have two distinct stages to their life. They begin as a gametophyte, with sperm-producing structures called antheridia and egg-bearing structures called archegonia.

The antheridia produce sperm, which travels through water to find the archegonia on another liverwort so that it can fertilize the eggs there. And when that fertilization happens, a new stage of liverwort emerges into the world called a sporophyte. It will continue developing in the archegonia until it’s ready to release spores into the world, which will develop into a new gametophyte, carrying on the cycle.

That process is so sweet and familiar: an egg and a sperm meet, and from there an entity develops into a life, expanding the world of liverworts just a little bit further. But thalloid liverworts are capable of reproducing by another means, a weirder one. All they need is a cup and some rain.

Remember that green swirl we saw earlier? That structure is on the surface of the liverwort, and it’s called the gemma cup. Its job is to hold little discs of liverwort tissue called gemmae.

The gemma cup and its little gemmae form during the gametophyte stage, but they don’t do anything at this point. The gemmae are simply dormant. So what does it take to awaken the gemmae?

Rain. Seriously, that’s it. When rain pours onto the liverwort, it splashes the gemmae out of its cup and carries them away.

And as they travel, the gemmae emerge from their slumber so that eventually, when they find a place to land, they become a new plant. Though maybe “new” is the wrong way to put it. They’re actually a clone of the old one, born from just a little disc carried in a cup and pushed out with just a dash of rain.

We have seen so many versions of asexual reproduction in the microcosmos, and they often feel kind of violent— or at least painful, if microbes felt the pain of tearing themselves apart into two identical clones. In comparison, the liverwort’s method feels so sweet, like it’s just packing its little future selves for a rainy journey. It’s a version of clones and asexual reproduction that we probably wouldn’t have conjured up in our wildest science fiction imaginations.

It’s adorable. A little bit of rain falls in a cup, and out comes a sleepy clone, ready to wake up and spread its wings, or, I suppose, its non-vascular body, into the world. Thank you for coming on this journey with us as we explore the unseen world that surrounds us.

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