Scientists at Teagasc have successfully copied two extremely rare shrubsplanted at the National Botanic Gardens nearly a century ago, writesDick Ahlstrom.
Two very rare flowering shrubs first brought to Dublin from China in the early 1900s have been rescued from oblivion after experts managed to propagate them. It took 18 months of careful work to coax material taken from the plants to grow into viable new "copies" of the two.
The original climbing shrubs have been growing outdoors at the National Botanic Gardens in Glasnevin since the turn of the last century. They are the only ones of their kind outside of their native habitat in China aside from plants held in a US collection, according to Dr Gerry Douglas, senior research officer at Teagasc's Kinsealy Research Centre where the work was done.
"Both are used in traditional Chinese medicines and we don't really know their population status in China," says Dr Douglas. Glasnevin was concerned that these rare plants might be lost from its collection despite possible uses in pharmaceuticals and as valuable ornamental plants.
Aristolochia chrysops, also known as the Dutchman's Pipe flower because of its unusual curved shape, was planted at Glasnevin in 1914. Sargentodoxa cuneata arrived even earlier in 1908. Over the decades, neither plant produced seeds even though male and female flowers were produced. Although the two acclimatised to Irish conditions, neither could be propagated from cuttings, the usual way to copy a plant.
"The problem with an old plant is it can get set in its ways," explains Douglas, who did the work at Kinsealy with John McNamara. No cutting could be encouraged to strike roots despite being given the best conditions possible.
The opportunity to try other methods arose because of an ongoing research effort at Teagasc to locate interesting old plants and shrubs that might be of value to plant growers. "The lifeblood of the nursery trade is variety," says Douglas. "We have cooperation going on trying to identify novel plants which may be of interest to the nursery trade."
Glasnevin knew of this work and asked Teagasc if they might be interested in the two venerable old Chinese specimens. Dr Douglas decided to use micropropagation, a method that involves the use of plant hormones, nutrients and carefully controlled growing conditions to coax small elements of a plant to grow to adulthood.
"Generally you would go for a bud because a bud would contain miniature leaves," he explains. Substances that promote growth are used "in very precise quantities" to encourage the bud cells to sprout and then to produce roots.
Micropropagation occurs in two phases, he explains, shoot formation and then root formation. First the bud is treated causing it to form a shoot and then this can be divided and treated with different hormones to encourage roots, hopefully delivering a viable plant.
This takes only days or weeks with many plants, but the two imports were very slow to cooperate. The few buds taken from each plant lived in various nutrients and acclimatised to these growing conditions for a full 18 months before finally forming their first shoots.
The Teagasc team managed to grow five or six plants of A. chrysops that are now growing happily in Glasnevin's greenhouses. "We still haven't got rooting on the material from the original S. cuneata plant," says Douglas. He remains confident, however, that they will also be able to encourage these half dozen shoots to go on and produce roots.
There is now no danger of S. cuneata disappearing from the Dublin collection, however, because Dr Douglas recently managed to get wild seed from China. The work done by centres such as Glasnevin and Teagasc has international importance given that globally there are more than 34,000 plant species known to have disappeared from the wild or facing extinction. "Decades of thoughtless commercial harvesting and destruction of habitats have led to this situation," says Douglas. "Botanical gardens are most important custodians of plant species," he says. "Worldwide, they grow 10,500 species that are threatened with extinction in the wild."
Plants such as the monkey puzzle tree, handkerchief tree and certain magnolias and camellias are now plentiful in Irish gardens, despite being rare in the wild, because of this work.
The two Glasnevin plants have another important historical connection. They were first described by the world-famous plant collector, Augustine Henry, from Cookstown, Co Antrim. He travelled China in search of plants from 1882 to 1888 and in all sent back more than 15,000 specimens to Kew Gardens in London and to Glasnevin.