The Island of the Colorblind

The forms of plants exercised Goethe endlessly – we owe the very word ‘morphology’ to him. He had no sense of evolution, but rather of a sort of logical or morphological calculus whereby all higher plants might be derived from a simple primordial type, a hypothetical ancestral plant he called an Ur-pflanze. (This idea came to him, he recorded, while he was gazing at a palm in the Orto at Padua, and ‘Goethe’s palm,’ as it is now called, still grows there in a house of its own.) His hypothetical Ur-pflanze had leaves, which could metamorphose into petals and sepals, stamens, and anthers, all the complex parts of flowers. Had Goethe concerned himself with flowerless plants, I could not help feeling, he might have seized on Psilotum as his Ur-pflanze.

Alexander von Humboldt was a close friend of Goethe’s, and adopted his theory of metamorphosis in his own Physiognomy of Plants (indeed, he widens Goethe’s notion and hints at a cosmic, universal organizing power acting not only on plants but on the forms of rocks and minerals and on the forms of mountains and other natural features as well). The physiognomy of the vegetable kingdom, he argues, ‘is principally determined by sixteen forms of plants.’ One of these – a leafless branching form – to his mind, binds together plants as diverse as the Casuarinas (flowering plants), Ephedra (a primitive gymnosperm) and Equisetum (a horsetail). Humboldt was a superb practical botanist, and very well appreciated the botanical differences between these, but he was looking, as Goethe was, for a principle orthogonal to biology, to all particular sciences – a general principle of morphogenesis or morphological constraints.

The arborization of plants originates not in accordance with some primordial archetype, but as the simplest geometric way of maximizing the ratio of surface area to volume and thus the area available for photosynthesis. Similar economic considerations may apply to many biological forms, such as the branching dendrites of nerve cells or the arborizations of the respiratory ‘tree.’ Thus an ‘Ur’ – plant like Psilotum, lacking leaves or other complications, is an exemplar, a diagram of one of nature’s most basic structures.

(In more recent times, a specific analog of Goethe’s theory, which traces how all higher plants might be derived morphologically from primitive psilophytes, has been proposed by W. Zimmerman, in his theory of telomes. And a general analog to Goethe’s morphology may be found in some of the current theories of self-organization, complexity, and universal morphogenesis.)

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Such a feeling of transport to the distant past struck Safford when he saw the cycad forests of Guam: their ‘cylindrical, scarred trunks, and stiff, pinnated, glossy leaves,’ he wrote, suggested ‘ideal pictures of the forests of the Carboniferous age.’

A very similar feeling is described by John Mickel, writing of horsetails:

To wander among them is a kind of science-fiction experience. I well remember the first time I encountered a stand of the giant horsetail in Mexico. I had the feeling that I had found my way backward into a Carboniferous forest, and half expected dinosaurs to appear among the horsetails.

Even a walk in the streets of New York can evoke the Paleozoic: one of the commonest trees here (apparently well able to resist pollution) is the maidenhair tree, Ginkgo biloba, a unique survivor little changed from the ginkgophytes of the Permian. But the ginkgo exists now only in cultivation; it is no longer found in the wild.

Darwin, in the Origin, introduced the term ‘living fossil’ to describe primitive organisms which could be seen as relics from the past – members of groups once widespread but now greatly reduced and occurring only in very isolated and restricted environments (where ‘competition…will have been less severe than elsewhere’). Ginkgos, for example, were very widespread once – they were a dominant species of the Pacific Northwest before the great Spokane Flood fifteen million years ago – but are now restricted to a single species, found only in cultivation and in a small area of China. The most spectacular discovery of such a ‘living fossil’ in this century was that of a fish, the coelacanth Latimeria, in 1938; a more recent one, which shook the botanical world, was the discovery in 1994 of a gymnosperm long thought to be extinct, the Wollemi pine, in Australia. (I still hope, in some irrational, romantic part of myself, that a giant club moss or horsetail will turn up one day.)