By definition a Botanic Garden has a variety of plants. But what is it that drives the marvellous variation in the plant world - the answer is adaptation.
Plants change their character, or adapt so they can survive in the wild. But understanding about plant adaptations can also guide gardeners in the care and maintenance of our own plants.
Two really good examples of adaptation are a jacaranda and a forest red gum Eucalyptus tereticornis. Both trees have adapted to winter drought, a characteristic of Brisbane's winters. But the trees have adapted in remarkably different ways.
The jacaranda, originally from central and south America, copes with the dry by dropping its leaves. No leaves mean no transpiration, so there's much less water loss. In comparison the gum has many means of coping with winter drought. These include vertical leaves, which present less surface area to drying sun, a thick leaf tissue, fewer breathing pores and a waxing coating on the leaves - all of which help to prevent water loss.
The forest red gum exudes compounds called saponins all over the bark. During rain it's possible to see soap like compounds forming foam at the base of the tree. These are natural wetting agents and enable water to penetrate the soil. What an incredible adaptation for survival.
But how do adaptations come occur? These plants reproduce sexually and during fertilisation, have an opportunity to inherit characteristics from both parents. Each succeeding generation results in perpetuating characteristics that aid survival. Any unhelpful characteristics are masked or die out.
Some plants have evolved the ability to take advantage of rainfall. For example mock orange, Murraya paniculata will grow rapidly in warm wet conditions. But in dry conditions, it will rest. Gardeners growing mock orange will notice that when useful rain is coming, the plants produce a burst of small, sweetly scented flowers. This is an adaptation enabling mock orange to make best use of rain to develop its fruit. The flower alert is also handy for the gardener. It's a reminder to mow your lawn before wet weather arrives.
Many plants we grow have adapted to cultivation. They adapt to garden soils and different climates from those in which they've naturally evolved. That allows us to make generalisations about entire plant groups, such as cycads.
Some cycads naturally occur in tropical rainforests, others in semi-arid regions. But wherever they come from, they benefit from freely draining soil. So make sure your cycad has a really gritty mix. Cycads store food and water in their stems, an adaptation to help them survive variable seasonal conditions.
For example the sago palm, Cycas revoluta can endure extended drought. But during warm wet weather, it can produce a burst of growth and almost double in size. This sudden burst of growth is believed to be an adaptation to protect them from grazing by dinosaurs. The tender young fronds rapidly harden to become less edible and they're also toxic, making them less palatable.
For the home gardener, it's better to water less during a resting period. But to maximise a burst of growth, give them a good feed and one or two good waterings.
Another example of an adaptation can be found on a creeping fig Ficus pumila. Young plants have beautiful foliage and that's why people grow them. But at maturity these plants take on an entirely different form. The creeping fig has adapted to grow up trees and it will climb to reach the top of trees. It's important to position creeping figs correctly and keep them well trimmed to keep the juvenile leaves.
The plant world is constantly moving. Plants have adaptations to help them survive. The more we learn about these adaptations, the better we become in caring for our own plants.