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Friday, 18 July 2014

About leaves

In my spare time, I am a volunteer in the Nursery group at a local sanctuary on North Head. We concentrate on raising plants and restoring damaged bush, and from time to time, I contribute a piece to their newsletter.  I don't think they are very accessible there, so I will pop them in here as well.

Lomatia sp.

Johann Wolfgang von Goethe had a bit of a thing about leaves. He wrote a poem about the leaf of the Ginkgo, and probably saw the leaf as a symbol of love. Goethe was many things, and also a curious botanist—some might say a peculiar botanist. He thought the leaf was the basic unit of the plant: "from top to bottom a plant is all leaf…".

Banksia sp.
I thought of this when I sighted a Lomatia along one of the tracks a few weeks back. At least, I think it was a Lomatia, but now I have my doubts, because of where it was growing. I'll need to visit it later in the year to check the flower, but Lomatia is one of those once-seen-never-forgotten leaves.

That started me thinking about distinctive leaves, like Canada's maple leaf, the serrated leaves of the Banksia and the gracefully curved leaves of some gums. Again, once seen, never forgotten, though I'll bet that somewhere out there, some other plant has taken on a similar design.

Allocasuarina, or she-oak.
That's why botanists, both before and after Goethe, used flower parts for identification, despite Goethe's ideas. Still, leaves help in identification, and they are certainly worth attention.

A leaf is just a plant's way of catching sunlight, while hopefully not losing too much water. Most Australian plants have tricks to hang onto their water. She-oak needles are really branches with the leaves tightly attached, all except for little scales sticking out.

Every walk brings me "leaves" to admire, but some are fake leaves like those on Bossiaea which are really cladodes, flattened stems. The leaves of wattles are often phyllodes, flattened petioles or leaf stalks, and in each case, the change is designed to save the plant from losing water.
Bossiaea sp.

Another way to avoid losing water is to discourage animals from eating the leaves. Biting a leaf opens wounds that the plant "bleeds" from, and what is eaten represents a loss as well.

That explains the rainforest leaf below, which I saw on the Dorrigo Plateau.

It has remarkably nasty spines to keep larger browsers away, though as you can see from the picture on the right, below, small animals just dodge around the spines and much away.

One of the things that changes the form of leaves, that shapes them, is what Charles Darwin called the struggle for existence against predators, though another aspect is the fight against other plants to get a place in the sun.
Listen, young Goethe, forget about plants as symbols of love.

Even the leaves remind us there's a war on out there. Some leaves are even mined!

Unnamed leaf which has been attacked by a leaf miner.

1 comment:

  1. You are a busy little blogger, McManly. Just love your stuff :)