Nature today | The nature of the pavement: low

During the last hot weeks there were many dried out pavement plants – they have already sown their seeds. But we also saw the necessary plants, looking beautifully fresh, in the middle of dry grass or hot pavement. The sharply drawn shadows seem almost works of art. More elaborate life forms can be seen on these tiles. Round discs in yellow, gray and blue. If you’re not looking closely, you might mistake them for crushed chewing gum. But they are low. You can also find them on poles and trees, often in the company of mostots.

urban nature

We have recently become interested in the mosses and lichens. With the support of Friends of the Leiden Hortus, we are participating in a project starting in October this year, under the title HiddenBiodiversity. Many parties are connected, and the tasks are distributed. Hortus will deal with, you guessed it, moss and lichen.
But let’s be honest: We don’t know much about that yet at Hortus. Coincidentally, biology student Harold Timans did an inventory of lichens at the Leiden Hortus in 2021 and 2022 as part of an internship. He found 111 species! The article about this was recently published in the specialist moss and lichen magazine Buxbaumiella. In a botanical garden, the climate is naturally a bit more pleasant for mosses and lichens, due to the variety of substrates and the fact that it rains. But there are also many mosses and lichens elsewhere in the city.

Mossy beech trees in the rain (Source: Hanneke Jelles)

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What are they good for, a visitor recently asked me. Of course, everything doesn’t have to be good for anything, but it might help to create awareness for these small townspeople. I had to think about the usefulness of lichen for a while. The answer can be quite simple: They provide shelter and food for all sorts of small urban animals and slow down the water runoff. They make the environment favorable so that plants can settle there. They grow on stones, poles or trees, but use them only as supports: they live on the air, from which they get their food and water.
Lichens can survive in places where even a sidewalk plant cannot stand, and provide food and shelter there. And they have another special quality: they are sensitive to their environment, and they tell us something about it. How old is the place of growth or how clean is the air. Read, for example, what Laurens Sparrius wrote about yellow lichens and nitrogen.


Quay wall with low and fine beam

Lichen is a real survivor, combining the properties of fungi and algae or blue-green algae. In fact, fungus and algae have grown together so much that they cannot survive without each other. It was discovered about a hundred years ago that a lichen consists of fungi and algae. Algae is a plant that can make sugar with the help of sunlight, it can do photosynthesis. The sponge ensures the absorption of water and minerals. The fungus forms a protective layer around the algae and secures the shape of the lichen. There is much more to say about it and we hope Harold Timans will do so in this place in the future. In October, a PhD candidate also starts a four-year study in mosses and lichens in the city at Leiden Hortus.

Orange rind and purple dish

When I was young, naming a lichen was quite difficult and involved all sorts of chemicals. Today, you can go a long way with the ObsIdentify app. In addition, lichens now have Dutch names. They are just a little easier to remember than scientific names.

Lichens and mosses on the smooth bark of a beech tree

The namesake brothers have been helpful with beautiful names such as purple dish, antler moss, witch’s finger moss and orange peel. If you want to practice a little, go hunting for lichens in Hortus with Harold’s lichen bingo (pdf: 165 KB). If you already want to know more about the hat and the shade, you will find good information here.

Tips are welcome, research continues

It is not yet October, our PhD candidate and the project have yet to start. The great new lav guide from KNNV Publishers will also be published in October, you can already reserve one now. And if you visit the site, the Stoeplantjesalbum is a nice gift for yourself and others. Anyway, a question for you: what tips do you have when it comes to lichen? And above all: what are you wondering? As a botanical garden, what should we tell our visitors about lichens? Think with us and tell us:

In the meantime, don’t forget to enjoy the sidewalk plants. In this dry season they have fruits and seeds in all kinds of shapes or sometimes they are still fresh and full of flowers. Sign them up for the Sidewalk Plant Survey, which will continue for years to come.

Text: Paul Keßler, Hortus botanicus Leiden
Photos: Hanneke Jelles, Hortus botanicus Leiden

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