Only a ? in a Guilded Cage
Have you ever seen a plant growing inside a cage? We saw such a sight at the Royal Botanic Gardens in Sydney, Australia. It makes you stop and think doesn’t it? Is the cage there to protect the tree or to protect the people? Is this some sort of carnivorous threat or what? The little evergreen tree inside the cage is actually a very non-threatening 50 cm tall. The cage is there to prevent anyone from running off with the rarest known tree species on earth. The existence of this highly unusual tree, known as the Wollemi Pine, was just discovered in late 1994. Scientists are still dancing with delight.
Certainly biologists had no expectations of finding anything unusual as they set out to explore the landscape in a national park in south eastern Australia. Exploration is fun but it can be tedious and dangerous too. Only a short distance west of Sydney, Australia’s largest city, Wollemi National Park nevertheless remains largely undisturbed. Few people are interested in visiting a sandstone plateau where the rock is criss-crossed by hundreds of narrow canyons, some only a few metres wide but perhaps hundreds of metres deep. Nevertheless for biologists like David Noble who do explore the region, the wild landscape provides plenty of interest. On the sandstone cliffs above, the only trees and shrubs which grow are those able to cope with dry soils and low nutrient levels. In the canyons below, however, conditions are quite different. Though the soil is still poor, lots of water collects. Thus the canyon floors typically contain warm temperate rainforest plants. Since the canyon walls are steep and the valleys narrow, many of these plant communities remain unvisited. It was during the course of such exploration in late 1994 that David Noble noticed some strange litter on the floor of a remote canyon. It seemed as if the trees had shed entire branches rather than simply leaves. Looking up, the biologist discovered conifer trees with a strangely exotic appearance. He didn’t know what they were. So he collected a branch for further identification. It soon transpired that nobody else knew what they were either. This was particularly surprising when one considers that the Botanic Gardens houses a fine large herbarium for identification of plant species. A tree, unknown to science, had just been discovered.
Wollemia nobilis is named for the national park in which the trees grow and, of course, for the explorer who discovered the two groves of tall slender trees. These groves include no more than 38 adult plants. Numerous seedlings of various ages are present at both sites so the future of the only stands known in the world does not seem to be threatened at present. But the excitement did not end there. This new tree is a representative of a plant family that includes only two genera presently living. Plenty of fossil representatives of similar plants are known, but only the two living genera are extant. Now suddenly the number has increased by 50 % to three living genera. In biological circles that is big news.
The new Wollemi Pine is actually not a pine at all, but a member of the plant family Araucariaceae. Fossil specimens of plants from this family are found in similar rock layers to those which contain dinosaurs (Mesozoic rocks). The first living tree species discovered was the Monkey Puzzle Tree (Araucaria araucana) from the Arauco region of the Andes Mountains in Chile and Argentina. Like other conifers, Araucarians have needle-like leaves. However in some cases these are so wide as to appear almost like broad leaves. They have male cones producing pollen and female cones producing seeds (no flowers are involved). The female cone of Wollemia is similar to that of the extant genus Agathis, while the leaf form is similar to that of Araucaria of which Norfolk Island Pine is the best known example. In addition the new plant has many other features which are unique. It sheds primary branches rather than leaves. The bare trunk then sprouts new growth from under the bark. Large mature plants have multiple trunks of different ages, each with leaves born in artistic flatish crows rather than pyramidal tips so typical of the conifers we know.
Not surprisingly the new discovery has provided a bonanza of wonderful research topics. The ecology of the trees is being studied. So is their growth form and their physiology. Biochemists are comparing their DNA sequences to those of other plants in the family. Also specialists are working on producing lots more of these beautiful trees. They are rooting cuttings, germinating whatever seeds they can obtain, and attempting to develop tissue cultures using sterile techniques.
A most interesting question remains however. Why is this plant here at all when it is so rare that only 38 adult plants exist (as far as we know). Obviously these trees must have grown in much broader regions of the landscape in the past. Presumably with changing environmental conditions they managed to survive in only one tiny area. One wonders how long such a precarious existence could continue. A period of a few thousand years seems in the realm of the possible. Standard interpretations of geological history suggest that most similar species have been extinct over a period of tens of millions of years. That seems a bit much, to say the least, for a tree for which we have no former record at all. The Wollemi Pine is another fascinating example of a supposedly ancient plant (living fossil) – rare, very much alive but vulnerable to local disasters which could have eliminated it altogether. I would not want to bet that the Wollemi Pine could last by itself even a few more thousands of years. (Imagine how poor the prospects would be for millions of years.) The rush to bulk up population numbers indicates that other scientists think the same thing. The continued discoveries of living fossil organisms in extremely small populations is an important indication that the history of life has been short since fossil beds containing relatives were laid down in the past.
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