Soon after the discovery of the Wollemi Pine, our researchers at the Australian Botanic Garden Mount Annan began developing propagation techniques to establish a collection of plants that reflected the trees growing in the wild. This horticultural research project established a population of plants for further research and translocation and provided material for commercial development of the Wollemi Pine (See Protecting the critically endangered Wollemi Pine).
We have investigated the growth of the Wollemi Pine from the very earliest stages of seed fertilisation, through to the germination and growth requirements of these spectacular plants. We have also banked seeds at the Australian PlantBank as part of the conservation strategy.
Pollination and embryological (seed) development
The Wollemi Pine is bisexual (monoecious), like its closest living relatives, with both male and female cones on the same tree. The round female cones produce the seeds, and the long male cones produce the pollen.
Male and female cones appear on separate branches, at the very tips. The female and male cones start growing in mid-summer. In late spring the male cones release masses of pollen, which is carried by the wind, to fertilise the egg cells in the female cones. The female cones then take about 18 months to ripen, when the fertilised ovaries develop into seeds and they then fall apart high above the canyon floor, releasing winged seeds that float to the ground. Each conifer seed has a scale associated with it. Like Agathis, Wollemia seeds are separate from the scale, whereas the seeds of Araucaria are attached to the scale. Both Agathis and Wollemia have winged seeds, but in Wollemia the wing encircles the seed and in Agathis the wing is one-sided.
Embryological studies tracked the sequence from fertilisation to seed development, using ultra-thin sections cut from dissected Wollemi Pine cones. These sections were mounted on glass slides for microscopic examination or prepared for examination using a scanning electron microscope. These studies were supported by the Hermon Slade Foundation.
Field observations and laboratory experiments indicate that following seed shed in summer and early autumn when temperatures are high, Wollemia nobilis seeds germinate, especially if exposed to light. The seeds that remain ungerminated or that are shed late in the season survive over winter, but germinate rapidly once temperatures rise in the next spring.
Constant-temperature experiments found that seed germination of Wollemi Pine proceeded most rapidly at temperatures between 24°C and 30°C. Few seeds germinated when incubated for 112 days at 10°C and 16°C but these later germinated when transferred to 24°C, whereas seeds initially incubated at 35°C were killed. Unstratified seeds showed a pattern of prolonged germination taking 130 days to achieve 40% germination at 24°C and 40 days at 27°C. Seeds stratified (chilled) at 6°C for 14 days and incubated at 27°C in the light achieved 40% germination within 20 days while those incubated at 10°C and 16°C for 112 days and transferred to 24°C achieved 40% germination by 15 and 24 days respectively. Initial germination of unstratified seeds was fastest when incubated at 30°C in the light, averaging 23 days.
Exposure to 12 h diurnal periods of 10-15 µmol m-2 s-1 light significantly increased 28-day incubation germination percentages, but only those incubated at 30°C. Additions of gibberellic acid (GA3) at 1mM had no effect on seed germination of W. nobilis.
Abstract from *Offord C A & *Meagher P F, 2001, ‘Effects of temperature, light and stratification on seed germination of Wollemi Pine (Wollemia nobilis, Araucariaceae)', Australian Journal of Botany, 49:699-704.
Seed cones mature in late summer and autumn and appear to be produced annually. Approximately 10% of seed produced in two consecutive years was viable, 25% of which was damaged by animals. Glasshouse studies showed that seed germination at 25°C day/16°C night proceeded slowly but steadily at approximately 4% per week until, after 6 months, 88% of apparently viable seeds had germinated with the remainder of the seed rotting.
Growth of potted seedlings in this temperature regime was continuous (after a lag period of 4-6 months) with the monopodial axis growing 0.05-0.25 m in the first year, 0.5-0.6 m in the second year and 0.25-0.35 m in the third year, attaining a total height of 0.8-1.2 m. Multiple orthotropic shoots developed on some plants at this stage, some of which outgrew the primary shoot in height. The diameter of the stem below the cotyledon (just above the soil) grew 3-7 mm in the first year, 10-14 mm in the second and 15-20 mm in the third at which time it was 25-34 mm.
The average number of lateral branches produced was 5-17 in the first year, 25-36 in the second year and 24-30 in the third year giving a total of 60-77. The establishment of Wollemi pine in the wild does not appear limited by the inherent viability of seeds and potential for early growth of seedlings.
- *Offord C A, *Porter C L, *Meagher P F & *Errington G, 1999, ‘Sexual reproduction and early plant growth of the Wollemi Pine (Wollemia nobilis), a rare and threatened Australian conifer’, Annals of Botany, 84: 1–9.
* indicates staff and students of the Royal Botanic Gardens Sydney