Photo of snowy Sussex woodland trail Photo of snowy Sussex woodland trail

Why are some leaves red?

Why are some leaves red and what does it mean?

We assume leaves to be green, but also notice how there are exceptions – we expect a show of reds, golds and yellows each autumn.

But what about all those red leaves we see turning up at other times of the year, even in the middle of summer?

The red colour is caused by pigments called anthocyanins. The pigments cause not only the red of some leaves, grapes and onions, but also the blue of blueberries and the black of soy beans.

Some trees are naturally very high in these pigments and will have strong colours at all times of the year. These trees are usually marked out by both their appearance and their name, eg. the copper beech:

Most plants have naturally low levels of these pigments and appear green most of the time. However, in certain situations these ‘green’ plants will produce higher levels of anthocyanins leading to a change in colour in their stems and leaves.

Many species produce young leaves that are red, which then lose this red colour as they develop. Like these young hazel leaves: 

One of the main causes of all red leaves is high levels of direct sunlight. And this is where it gets interesting for natural navigation.

Trees have two types of leaves: sun leaves and shade leaves. And only sun leaves are likely to have raised levels of anthocyanins and therefore to turn red.

We see more red leaves in direct sunlight and that is much more likely on the southern side of plants.

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