Thursday, December 13, 2012

A cold-tolerant eucalypt

Species name: Eucalyptus gunnii

Common name: cider gum, eucalyptus

Location: Ontario

For anyone from Australia, to see any eucalyptus plant in Canada outdoors would probably be surprising. In fact, it's not just Australians that would be surprised; this Canadian was mighty surprised, too. I was shocked to see that the campus landscapers would have thought this plant was going to survive in our climate, which is inhospitable to tropical trees to say the least. To my surprise, the more I read about this plant the more I wanted to put one in my back yard for novelty sake; it's actually incredibly cold tolerant! This species of eucalyptus will readily survive winters with extended periods below -10 degrees Celsius, and can even survive short periods below -20 degrees Celsius. It's still not a good idea to trust this plant to a harsh Canadian winter, but finding out it could survive snow cover was a surprise to me. This is actually becoming a popular garden plant in Europe since it has the attractive evergreen foliage of a eucalyptus (and the incredible smell) while not having to be taken indoors every winter.

All eucalyptus trees are native to Australia and the surrounding area, but most have been successfully transported outside of this restricted area for ornamental and medicinal use. This particular species, the cider gum tree, is native to a very small area in Tasmania. Like Madagascar periwinkle (which you can read all about HERE), there are few individuals left in the wild in its native range, despite being so incredibly common in other locations in the world due to its ornamental value.

One spectacular morphological characteristic of this plant that is rarely seen to this degree in nature is the morphological variation of the leaves along a single branch. The leaves start off almost circular, with a very short (sometimes absent) petiole at the base of the leaf. The leaves spiral around the branches of the tree, and are a brilliant grey-green. As the branch grows longer, the leaves also elongate until they look very similar to willow leaves, and there is a change in colour so the leaves are a much darker, deeper green. If the tree is pruned into a shrub (as is most common in an ornamental plant setting), the shrub will retain its juvenile leaf form and never progress to having elongate leaves.

While this species of eucalyptus is not often used for anything other than as an ornamental plant, other species in the genus are used for their essential oils, which are very powerful antibacterial chemicals, insecticides, and even industrial solvents. The oils are sometimes also added to food, but only in very minute quantities (the saying "a little goes a long way" is absolutely true in the case of this plant, but also even moderate amounts of the essential oil when consumed is toxic to humans). The tree's leaves are the main food source of the koala, an animal often regarded as the "icon of Australia". Eucalyptus trees are also known as "water-suckers" since they can completely dry up a swampy area in only a few years, turning the soil into arable land. This doesn't last long, however, and the land quickly converts to desert after only a few growing seasons. The wood of eucalyptus trees is very quickly produced, and so it was once considered as a biofuel before being abandoned for other crops that were easier to care for.