Plaque in the park overlooking Wyndham delta, Western Australia.
Native PlantsPlants

Boab – a weird one!

By Clive Larkman

The world of plants is wide, weird and wonderful. I have been writing these articles for over sixteen years and they have mostly been on edible or medicinal plants, some of which have been a bit odd or at least one known to western gardens. Some have been edimental plants;  both edible and ornamental.

This month is an edible plant (according to the indigenous folk of the Kimberley Region of northern Western Australia and western Northern Territory) with an interesting shape. The leaves, seed pith and roots are all a major food source for local indigenous groups.

Large tree in the main street of Wyndham, Western Australia
Large tree in the main street of Wyndham, Western Australia

The Boab, Adansonia gregorii, is the only Australian Bottle tree in this genus. There are five other species in Madagascar and two in mainland Africa. The genus is generally referred to as Baobab but for some strange reason we shortened the name for our endemic plant to Boab. The original word is an Arabic word meaning ‘father of many seeds’.  They also have the common name of Bottle Tree in reference to the unusual shape of the trunk and the ability of the tree to store water. They have a range of names in Africa and Madagascar and several common names in Australia including: Cream of Tartar tree, from the flavour of the pith in the seed pods; Gourd-gourd tree from the shape of the trunk and its water holding ability; Upside down tree due to the shape of the trunk and the way the branches spread. Plus, some of the Indigenous names are Jumulu, Gadawon, and Larrgadi.

There are many oddities in the Boab. Australia has only a few deciduous trees, Boab, being one of them, but unlike the European trees that drop their foliage to help survive the bitterly cold winters. Adansonia drops its foliage early in the dry season and re-foliates just prior to the arrival of the wet season. It is a true Angiosperm producing plenty of large white fragrant flowers at the change from dry to wet season. They open at night and are pollinated by hawk moths and large black fruit bats.

The seed pods are quite large (size of a large mandarin) with a hard, brittle, skin that is covered in a fine brown fuzz. Inside is a white pulp that tastes like cream of tartar and holds lots of small, irregular shaped white seeds.

The African varieties are some of the oldest documented Angiosperms in the world, with one specimen being carbon dated at around 2400 years old. The oldest Gymnosperm is reputably Bristlecone Pine in the Californian Rockies at 4800 years old. These are easier to date as they produce annual growth rings. It is the thick trunks of Baobab trees that give them their distinct appearance. The Boab is smaller than the African species at only 5 to 15m in height and up to 5m in diameter. One of the African species, Adansonia digitata, grows up to 25m high and with a diameter of up to 10m.

There are three theories on how Adansonia gregorii came to Australia. The first theory is a common ancestor going back to Gondwanaland. The second is that the seed pods floated across the ocean, and the third is the seeds were brought here by early man travelling across what would have been a hotter world. The nature of the soft ‘wood’ has meant there aren’t any fossil records to suggest which theory is most likely.

The Baobabs have a different internal structure to most vascular trees. It has been thought that the trunk is used to store water from the wet season for use during long dry, when they can have extended dry periods. Indigenous people in both continents have drawn water from the tree during the dry. It is believed that if too much is taken the plant will stress and the trunk will become weak.

Grafted Adansonia gregorii as referred to on the plaque
Grafted Adansonia gregorii as referred to on the plaque

The trunk wood is soft and less dense than other trees and the water content in the trunk is so high the wood to water ratio can be as low as 1:10. The water content in the cells helps give the tree its strength and can change during the year. The outer bark maintains its rigidity by keeping the water content of those cells high all year. If the water content internally drops too much the tree can collapse under its own weight. It is this peculiar habit that enables (requires?) the Boab to have such a high diameter to height ratio.

It is also the ‘wet’ outer bark cells that give the plant another odd characteristic in that carvings in the bark stay visible for hundreds of years. In 2020-2022 a survey of the carvings in the Boabs was conducted and there many similarities to these and the indigenous rock paintings. These carvings are known as dendroglyophs. More so than most trees, there are registered specimens of individual trees in northern and western Australia.

There are some famous boabs too. One is from the area where the rivers flow into the Timor Sea north of Wyndham in Western Australia. Here, a Western Australian botanist made a successful attempt to take a cutting and graft it onto rootstock, and planted it in a park overlooking the nearly deserted town of Port Wyndham. Another tree in the Wyndham Caravan Park is promoted as “the biggest boab in captivity”.

There are two large hollow Boabs that were reputably used as prison trees. One is south of Derby and one is east of Wyndham, both of them in far northern Western Australia. The Derby tree was used in the 1890s as a lockup for Aboriginal prisoners on their way to Derby and is now a tourist attraction. The second is on the King River Road between Wyndham and Kununurra. The story is that the large trees were hollowed out and the Aboriginal prisoners placed in them overnight.

In 2008 there was a project commissioned to move a large boab down to Kings Park in Perth. It had to be moved from the site of the Great Northern Highway. The tree is called Gija Jumulu. Gija are the local people, and Jumula is their word for Boab, and the tree has settled in well at the park. It is a special tree at 760+years old, 18m tall and over 35 tons in weight. It was moved by truck over 3000km and is one of the greatest tree relocations worldwide. Currently, the tree is growing well and is visited by hundreds (or thousands) of people every year.

Finally, there is a tree on the road between Katherine and Kununurra called Gregory’s Tree, located in the appropriately named Gregory’s Tree Historical Reserve at Timber Creek. The tree marks the site of a camp of the explorer Augustus Gregory after whom the tree species is named. It is inscribed with the dates of his party’s arrival in October 1855 and departure in July 1856.

This is a classic case of the plant being interesting but the stories around its history are even more so.

All images supplied by Clive Larkman


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