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Thursday, 22 September 2016

About leaves

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

I thought of this when I sighted a Lomatia (right) along one of the North Head 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 (left) 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. 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.

She-oak, Allocasuarina.
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 (right) 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 (left) which are really cladodes, that being a fancy name for flattened stems. 

Then again, 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.

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.

Rainforest leaf, unidentified.
That explains this rainforest leaf, which I saw on the Dorrigo Plateau, has such nasty spines, though as you can see, small animals just dodge around the spines.

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!
Leaf, attacked by leaf-miners.
I think I might leaf it there.

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