Saturday, May 31, 2014

Thorny Yellowwood

Zanthoxylum brachyacanthum
What is this plant’s future?

Here’s the trunk of a young thorny yellowwood, showing what a prickly little fellow it can be. Those thorns are sharp!
Like human teenagers, it will grow out of this prickly stage.
In older trees, the thorns thicken up and lose their sharp points. You can put your hand on the trunk of a mature tree, quite comfortably, even though it is still covered with the fat old thorns.
Notice the young vine in the photo above. Perhaps this yellowwood sapling will grow into a strong tree, up to 15 metres tall in its rainforest environment...



...or perhaps its future will be like that of the plant at right.

This one’s broad thorns tell us that it is actually quite an old plant, but life in the stranglehold of its encircling vine has not been easy. It hasn’t reached the size we might expect for a plant of its age.

Here's the trunk of a large specimen.

Thorny yellowwoods are pretty plants. Grown in optimum conditions, they become attractively shaped trees with dark, dense canopies, like this one at Peacehaven Botanic Park which I photographed three years ago.
Thorny yellowwoods grown in gardens, where they don’t have to compete with tall trees for light, will never reach the height of their rainforest relatives. 6-8m is a more likely maximum for a garden specimen. The plants are dioecious, so the best way to grow them might be in a grove of 3-5 trees, planted close that their canopies unite into one. This would give a high likelihood of having plants of both sexes.
They contribute to the environment by hosting swallowtail butterflies, and (in the case of fertilised female trees) producing shiny black seeds in bright red follicles to attract birds.

The Peacehaven plant is female, as these flowers show.

Australia has six Zanthoxylum species, all but this one being plants of the tropics. They all have aromatic bark, leaves and seed follicles.
Spices have been produced from most of the 250 or so overseas species of Zanthoxylum. For example, Sichuan pepper, one of the ingredients of Asian five-spice powder, is produced from the red follicles of any of several Zanthoxylum species. Young leaves and shoots of other species are used as garnishes or as an ingredient in a strongly flavoured pesto-like paste. Even the bark is used in small quantities for flavouring.
I am not aware that our local species has been used for any of these purposes, but the potential may be there.

The Rutaceae Family
This family is well known for the strong smell of its members' aromatic leaves.
Some smell wonderful, and some quite appalling.
It is a Gondwanan family, only one branch of which, (the one containing citrus fruits) has spread to any extent into the Northern Hemisphere.
Knowing the family of a plant can help us to know how to manage it, as a garden plant. Australian Rutaceae would rather you didn’t fertilise them. They are well-adapted to low-nutrient soils.
To find blogs on other local Rutaceae, search for the family name in the white search box at top left.

Wednesday, May 21, 2014

Leichhardt’s Ironbark

Bridelia leichhardtii
It’s interesting to see this tree at work.

Plants need something or someone to distribute their seeds about for them. Without this assistance, they would have thousands of babies with nowhere to grow but under their parents.
This tree, with its red fruits, is advertising for birds to do the job.
What it wants is for them to eat its fruit, clean its seeds, and deposit them, with a little dollop of fertiliser. It produces large numbers of fruits, so there is always a good chance that some of them will be dropped in a suitable site for growing.
Birds are attracted to the colour red. These particular  fruits are slightly translucent, and glow brightly in the sunshine, no doubt looking particularly appealing to any fruit-eating bird that flies past.
When it stops at the tree, however, it soon discovers that the red fruits are not yet ripe, but that the several black fruits scattered amongst them are soft, succulent, and no doubt delicious. Having learned this, birds are likely to return to the tree again and again during its fruiting season, spreading the fruits much more widely than they might have in just a few gorging sessions.
It is usually seen as a shady small tree, but can grow to have a prominently fissured trunk of as much as a 30cm diameter. It can also be a large, multi-trunked shrub.
It likes a well-drained soil, and can usually be found growing on hillsides, in red or black soil country.