Cabbage tree
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| Cabbage tree Conservation status: Secure | ||||||||||||||
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 Cabbage tree in flower, Dunedin Botanical Gardens | ||||||||||||||
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The Cabbage tree (Cordyline australis) or ti kouka, is a monocotyledonous tree endemic to New Zealand. It grows up to 15 m tall, at first on a single stem, but dividing into a much-branched crown, each branch forking after producing a flowering stem. The leaves are sword-shaped, 40-90 cm long and 3-7 cm broad at the base, with numerous parallel veins. The flowers are creamy white, each flower small, about 1 cm diameter with six tepals, and produced in a large, dense cluster 50-100 cm long. The fruit is a white berry 5-7 mm diameter.
Because their high carbohydrate content can be made digestible by cooking, they were a valuable food source for at least the first 800 years of the Maori occupation of the country. Radiocarbon dating points to use since about the year 1000. Related trees were probably valuable elsewhere in the South Pacific. Fern root was the only other substantial carbohydrate source.
The Otago Peninsula is one place where archaeology has shown substantial use of the cabbage tree for food. Huge hollows, up to 7 m across, are the remains of "umu-ti" (cabbage-tree ovens). After cooking for 2 days, the bundles of young cabbage tree would be sun-dried, in which state they would keep for years.
Cabbage trees also have value as fibre sources. The trunk and root material can be twisted into ropes, and the leaves can be woven for clothing and footwear fabrics. Juice from the plant has value for fighting infections. Early missionaries "brewed a tolerable beer from it". The commercial value remains to be fully examined. Possibilities are as a low-calorie sweetener (since it is twice as sweet as sugar) and as an ethanol source.
It is also widely planted as an ornamental tree, in New Zealand and also in western Europe (including the British Isles) and the west coast of North America. Because it tolerates colder weather better than many other tree-sized monocots, this plant is often planted by people wishing to give a tropical, exotic look to their yards or gardens. The overall visual effect is said by many to create a view reminiscent of a palm-tree (it is occasionally even mis-named "Torbay palm" in the British Isles).
A thesis on the uses of the tree was produced in about 1986 by scientist Barry L. Frankhauser. A documentary that includes an interview with him is in the New Zealand Television Archive and was broadcast in 2004 by Maori Television.
Since 1987, cabbage trees in New Zealand have been affected by a disease, which has been named "Sudden Decline", and usually leads to almost total defoliation of affected trees within 2-12 months. The causative organism of this is now known to be Phytoplasma australiense.