Cycads the living fossils of plant world

JOHN MEDLEY WOOD was a 19th Century sailor turned farmer who became curator of the Durban Botanic Gardens in South Africa.

In 1895, he stumbled upon a clump of four strange trees in a forest in KwaZulu Natal. The trees belonged to an ancient fern-like group, known as the cycads and were of a species unknown to science at the time. It was a remarkable discovery; no other Wood’s cycads have been found. Shoots of the trees were taken. They proved easy to cultivate and specimens now grow in botanical gardens worldwide.

In 1907, two of the original trees were removed to Durban and, in 1916, the last surviving trunk was taken into captivity. It died in 1964.

Ireland’s National Botanic Gardens has a Wood’s cycad. It’s in the beautiful curvilinear glasshouse, a suitable location for a celebrity. But there is a story behind this particular tree. According to Dr Mathew Jebb, it was collected in the 1890s, but misidentified at the time. Exported from South Africa under the wrong name, it was subsequently recognised as a Wood’s. The precise origin of the plant is not known, so it may not be an offshoot of the trees which Wood found.

Male cycads produce conspicuous orange cones. The Dublin tree has never produced these and there is, therefore, a chance that it is female. Wood’s trees were all male and so the specimens growing in gardens are male. A female Wood’s cycad would be a celebrity indeed.

The cycads were one of the earliest forms of tree. Non-flowering seed plants with thick trunks and long feathery leaves, they look a bit like palms, though they are not related to them. Cycads thrived during the age of the dinosaurs and were eaten by the giant reptiles. With the rise of flowering plants about 150 million years ago, they declined but there are still about 70 cycad species alive today. The best known of them are probably the so-called “sago palms” of Indonesia. Sago is a yellowish floury starch derived from the trunk of the sago tree, which was widely eaten in Ireland up to the 1960s. It is an important food plant in New Guinea and the Solomon Islands.

Since they first appeared on the scene about 300 million years ago, the cycads have changed little and are often regarded as living fossils. Plants need light for growth and cycads, like all trees, evolved out of competition for light. There is just as much light at ground level as there is up in the air, but the demand for more energy forced plants to develop stems so that they could lift their light-absorbing leaves above those of their neighbours. Tree trunks are the ultimate weapon in the struggle for light. But the earliest trees had a problem. Trunks need to be firmly planted in the ground, otherwise they will be toppled by the wind. There was little or no soil into which the early cycads could anchor their roots. Soil is the end product of plant decomposition; it would take countless generations of plants to produce the thick coating which we have today.

Ancients trees feature in an exhibition Jurassic Bark — the evolution of the plant kingdom, which opened at the Botanic Gardens during Irish Geology Week and runs until June 16. The exhibition is a joint venture with Trinity College Geology Museum. It is the work of two brothers: Dr Peter Wyse Jackson, director of the gardens and Dr Patrick Wyse Jackson of TCD.

Ireland played an important part in the discovery of ancient plants. In the 1970s, John Feehan, then a postgraduate student at Trinity College, made an extraordinary discovery. On a hill near Moneygall in Co Tipperary, he stumbled on some ancient fossils. Dated to 420 million years ago, they were the petrified remains of the oldest land plants ever found. Called Cooksonia, after the palaeontologist Isabel Cookson, the earliest land plants shed their male and female spores into water, the way ferns and mosses do today. Then, a development occurred; some female plants began to keep their seeds attached to their branches, relying on the wind to carry male microspores to fertilise them. The age of seeds and pollen had begun and the way was open for trees to evolve.

Other freak survivors from the distant past also feature in the exhibition. Fifty million years ago, ginkgo trees were found throughout much of the world. Then they fell on hard times. The maidenhair tree is the only member of the family to have survived. A native of China, it was saved by its beauty. Ginkgo, apparently, means silver apricot in Chinese and Chinese monks planted it in monastery gardens. Extinct in the wild, it now survives only as a garden tree.

The dawn redwood is another ancient Chinese survivor. A single tree was discovered in 1943 and shoots taken from it now grow all over the world. The most recent addition to the Botanic Garden’s collection of survivors is the wollemi pine, which was found growing in a secluded valley of Australia’s Blue Mountains a few years ago. A specimen, enclosed in a protective cage, can be seen not far from the Wood’s cycad in the great curvilinear glass-house. Entry to the exhibition is free.

Congratulations to Fiona Ryan and to Marshallstown National School, Co Wexford, on winning this year’s Esso Wildlife Challenge.

The number of children who have taken part in the competition, since it commenced in 1992, is a staggering 210,000.