Advertisement

Ken Thompson: how buttercups can teach you the age of a meadow

English meadow flowers - Moment RF
English meadow flowers - Moment RF

As every schoolboy (and girl) knows (or should know, in an ideal world), you can date a hedge very roughly by counting the number of different kinds of trees and shrubs in it. Older hedges, on average, have more different species in them than young ones.

But just suppose you wanted to know the age of a meadow. Counting the number of different plants in a meadow is a job for an expert, and it wouldn’t help anyway, since there’s no simple relationship between number of species and age in this case. 

So how do you find the age of a meadow? I confess I wouldn’t have had a clue until quite recently. But the other day, while looking for something else altogether, I came across a bit of overlooked research from a few years ago in the journal Annals of Botany that tells you the answer. Actually, it may not have been overlooked at all, but it was certainly overlooked by me. And I think – I really think – you should know about it. It uses some really neat biology, it’s dead simple and, better still, it works.

The principle is that as any organism grows, and its cells divide, they accumulate tiny genetic mistakes: mutations. If these mutations accumulate at a constant rate we have the basis, in principle at least, of a clock. But we need the right plant, and the right mutation. 

Creeping buttercup  - Credit: Tim Shepherd/ Oxford Scientific RM
Creeping buttercup Credit: Tim Shepherd/ Oxford Scientific RM

Buttercups are a good choice. But not just any old buttercup, because sexual reproduction, followed by establishment of a new plant from a seed, resets the mutational clock to zero. So a plant that regularly reproduces by seed is no use; most of its individuals will be younger than the meadow, often much younger.

We have three common species of buttercup, and two of them, the bulbous buttercup and the meadow buttercup, reproduce frequently by seed. But the creeping buttercup does not; it mostly reproduces vegetatively (hence the name). So you can be reasonably certain that the creeping buttercups in a meadow are about the same age as the meadow. With a decent wildflower book and a bit of practice, the three buttercups are easy to tell apart. Creeping buttercup is the annoying weed that grows in your lawn, and your borders too, given half a chance.

The right mutation has to do something that we can measure easily. Most mutations either don’t do much, or what they do isn’t easily measured. It turns out that the perfect mutation is one that increases the number of petals in the flower. 

So, now we have the right plant, plus the right mutation, finding the age of a meadow could hardly be simpler. Look at 100 randomly chosen creeping buttercup flowers and count how many have more than the five regulation petals. Every flower with extra petals equals roughly seven years. So if you looked at 100 flowers and 14 of them had extra petals, your meadow is about 100 years old. Technically, of course, we’ve found the age of the creeping buttercups in the meadow, but we’re assuming that’s the same thing.

Good, eh? Just the thing to keep the kids out of trouble on a country walk while you’re eating your picnic, plus they learn some science and history, and you get to show how clever you are.

Ken Thompson is a plant biologist with a keen interest in the science of gardening. He writes and lectures and has written five gardening books. The Sceptical Gardener is a collection of his Telegraph columns (visit books.telegraph.co.uk).