Plants of the lost world

Forest and Bird, Issue 296, 1 May 2000, Page 38

Plants of the lost world

ANN GRAEME,

Story

illustrations TIM GALLOWAY.

strictly accurate, my daughter Kate found it. Newly returned from overseas, she was ‘tidying up the parents’ by weeding the neglected garden in the courtyard. I was working in a deck chair under the sun umbrella. ‘There’s a strange plant here, Mum, she said, fossicking amongst the kiokio fronds at the base of a tree fern. "You'd better have a look at it? I knelt down and peered under the ferns and there it was — Psilotum nudum — growing in my garden! ‘ found a treasure in my garden. To be

This may or may not amaze you, so let me explain. The genera Psilotum and Tmesipteris are the only survivors of a group of plants called Psilotopsida that have been around on Earth for more than 400 million years. Their simple forms suggest the first models for plant life on land. Psilotum nudum looks like an exercise in geometry. Each stiff little stem forks and then forks again, sprouting tiny leaves and bright yellow

balls of spores. It is a pioneer plant, widespread in the warmer parts of the world. In New Zealand it grows best in rock crevices or in the warm soil of thermal areas. Much more exclusive is the ancient genus Tmesipteris, which grows only in New Zealand, Australia, Tasmania, New Caledonia and some Pacific Islands. Four species flourish in this country, and all have a habit of dangling as epiphytes on the trunks of treeferns, just like they must have done in the ancient forests. Tmesipteris is the holy grail for botanists of the Northern Hemisphere. The television botanist Dr David Bellamy was once asked what was the highlight of his first visit to New Zealand, and he replied, ‘I have seen Tmesipteris!’

Another ancient group, a contemporary of the Psilotopsida, was the Lycopsida, whose present-day survivors are called club mosses or lycopodium. Our native club mosses are easy to recognise with their forked stems and furry or scaly leaves. Some scramble, one dangles, and several grow like miniature trees.

Affectation, or a twisted sense of humour? Tmesipteris and Psilotum? Looking at these Latinized names you may think that botanists are ‘eggheads. There may be some truth in that, but the naming process is a logical and standardised way to bring order to the exuberance of species in the natural world. The Latin language may be dead to most of us but it is non-parti-san and can be understood all over the world (by eggheads, anyway). So, for non-egghead readers: Tmesipteris is pronounced mes-ip-teris and means "divided fern, probably referring to its common but inaccurate name, which is ‘fork fern’. Psilotum is pronounced sigh-low-tum and comes from the Greek psilotum meaning ‘bald’ or leafless. Nudum is ‘bare’ or ‘naked. The ‘baldness’ relates to a characteristic of the genus which is leafless, and ‘bare’ is the species name. Certainly, Psilotum nudum is very bare indeed!

t the present time, world vegetation is dominated by flowering plants. They are the grasses in the paddocks, the vegetables and flowers of the gardens, the alpine plants and most of the forest plants. But it hasn’t always been this way. Before the flower and the cone-bear-ing plants evolved, back in the steamy swamps of the Devonian and Carboniferous eras, quite different forests grew. There were hundreds of different species of Lycopsida, trees more than 40 metres tall, some with stout trunks crowned with branches and others like enormous candlesticks. Other tall, tree-like plants were Calamites, of the plant group Sphenopsida, which are all now extinct except for the genus Equisetum, the horsetails. Amongst the forest trees grew tree ferns, the ancestors of our wheki and wheki-ponga, with Tmesipteris dangling on their trunks. Three hundred million years ago those Carboniferous forests would have seemed quiet to us, for this was before the advent of birds, and the great explosion of insect species was only beginning. There were no bees to pollinate the flowers, for there were no flowers to lure them. Only the wind dispersed the spores from the primitive trees, while prehistoric amphibians grunted and croaked in the swamp. The Carboniferous forests were vast and existed over many millennia. As trees died and fell into the swamp, their squashed remains created colossal coal deposits, locking up their carbon in a carbon ‘sink. In the natural carbon cycle, leaves take in carbon dioxide from the air and convert it to sugars by photosynthesis. Then, during respiration and decomposition, the sugar is metabolised into energy and carbon dioxide is released back into the atmosphere.

Now our species is using the coal deposits to fuel furnaces and power stations all over the world. Thus we are burning the accumulated carbon of millions of years of ancient forests, and in so doing we are releasing vast quantities of stored carbon dioxide, which traps the sun’s heat and warms our atmosphere. Past climate changes have often triggered mass extinctions, and past evolution has provided new solutions, though this may be cold comfort for our species. But Psilotum has lived through it all — the warm periods, the ice ages, the rise and fall of the dinosaurs — and I am glad to have it growing in my garden.

ANN GRAEME is national co-ordinator of the Kiwi Conservation Clubs, and lives in Tauranga.

Down but not out — some are pests! You might imagine that a species that is the last of its line, a living fossil in a modern world, would be frail, vulnerable, hanging on by its rhizomes, so to speak. This is certainly not the case for two species that are pests in New Zealand. The field horsetail Equisetum arvense is an introduced, invasive and aggressive weed that is presently naturalised on river banks from Kawhia to the Buller Gorge. Even more widespread is Selaginella kraussiana, (pictured at left) a lycopod from Africa that often grows in shade houses and in the potting mix around pot plants. Selaginella carpets shady banks and damp forest floors, suppressing native seedlings. It is very hard to get rid of and can only be exterminated with weed spray. Watch out for this pest of a ‘living fossil’ when you are buying plants and planting out native seedlings.