How might climate change affect herbal remedies?

With a changing climate, what could happen to medicinal plants?
28 September 2021


A germinating seedling



With a changing climate, what could happen to medicinal plants?


Ethnobotanist Cassandra Quave explains how medicinal plants could be at risk...

Chris - Cassandra, you go all over the place hunting for plants that have exciting medical properties. Presumably one place you can start is to ask the locals?

Cassandra - Yeah, absolutely. That's one of the main ways that ethnobotanists learn about the uses of plants is through interviewing locals or also looking at historic literature. We've looked at records going back to the 1600 of plant uses in different parts of the world

Chris - One thing that's got me concerned is that you're doing this work, but the plants that those locals know about may, thanks to the effects of climate change, not be there for much longer

Cassandra - Absolutely. We're facing a crisis on a global scale when it comes to the impact of climate change on the availability of many of these plants. I can give you some statistics on this. We know that there are around 374,000 species of plants on earth and roughly 9% of those are actually used as medicines by people. When we think about plant based medicines in the west, we often think of herbal teas or dietary supplements or these kinds of commercialised versions of these. Actually billions of people across the globe rely on plants as their primary form of medicine. They're acquiring them through harvesting them in the wild during peak seasons of when they're in flower or fruit and then storing them throughout the year in their home, or growing them in their gardens. For those wild harvested plants there are challenges that are rising as we see ecosystems impacted. When you think about the optimal climatic zone, the optimal elevation point at which different plants grow, as climate change and environmental factors encroach you start to run out of mountain as the plants migrate up. Yeah, there are some serious problems with supply.

Chris - Somewhere I read that about a third of the drugs that are in the top 10 of things that are in your average doctor's bag or your average hospital formulary have their direct roots in nature and in plants

Cassandra - Absolutely. The World Health Organisation has a list that they come out with. It's called the World Health List of Essential Medicines. If you go through that list you can see many examples of drugs that we use today to treat cancer, heart disease, pain, malaria, infection, all types of different diseases and the chemicals that are used in those drugs and the structural blueprints for many of those cases were originally derived from plants.

Chris - Why do plants need an anti-malarial though? Just to take an obtuse example, what's it doing in the plant? Is it just luck that the same molecule, when you put it into us helps to treat malaria and in plants it does something different? Or are there some shared characteristics, so plants make these things to ward off the same sorts of problems that we get?

Cassandra - First we have to set this idea that plants are really some of the best chemists that exist on earth. They have this amazing slew of compounds they produce. Even in a single leaf tissue you may have hundreds of distinct molecules. Some of those molecules are useful for processes of photosynthesis and just simple growth and reproduction. But many of them are what we call secondary metabolites. These are the compounds that plants use to defend themselves from pests and from herbivores that get a bit too greedy as they munch on their leaves. Any kind of animal that gets a bit too munchy, plants can actually change their metabolism. They can actually upregulate and start to produce higher levels of poisonous compounds in their leaves to deter or repel other organisms that are harming them. In the same sense they can release compounds that attract pollinators and seed dispersers. I like to use the example of the corpse plant. I don't know if the audience is familiar with that, but this is sometimes in botanical gardens and they call it Mr. Stinky, it's a titanarum. When it blooms, it has this amazing smell of a rotting corpse.

Chris - I like Ella's face when you said that! Said it all, but they did have one of those at Cambridge University. They don't flower very often do they? It took decades before this one was big enough to flower, apparently the smell was really something to write home about.

Cassandra - Exactly. They're found in the wild in Indonesia. I came across one, not in flowering state but in its leaf form once in the forest. It was just amazing to see it. I felt like I was a fan girl. It poses this question of why does a rose smell like a lovely rose? Why does this titanarum smell like a rotting dead body? It all comes down to those chemical signals. They have different pollinators. Different organisms need to come to them because plants are sessile, they can't get up and move away from threats or go towards resources that they need. They rely on these chemical signals to really recruit or repel other players in the ecosystem.

Chris - Amazing stuff, Cassandra, thanks very much.


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