Landcare Research - Manaaki Whenua

Landcare-Research -Manaaki Whenua

Tī kōuka

Māori names tī, tī kōuka, tī rākau, ti whanake
Other common names cabbage tree
Scientific name Cordyline australis
Family Laxmanniaceae

Tī kōuka is a familiar and distinctive feature of the New Zealand landscape. The fibrous leaves are not used so often by weavers today, but are still valued for their toughness and durability.

Snares made from tī leaves were durable and kept their shape well. Because tī fibre doesn’t shrink in water, the leaves were used for anchor ropes. Fishing nets made from harakeke were strengthened with runners of tī leaves. Kawe (back straps) for carrying heavy loads were often plaited from tī. Paraerae (sandals) made from dried tī leaves were a valued item for traversing rough ground and avoiding prickly plants underfoot.

Distribution

The cabbage tree is widespread throughout New Zealand, and commonly found on forest margins, open spaces, river terraces and in wetlands. Their resilience out in the open means that they are often a feature of farmland.

Description

A young cabbage tree has a single, slender trunk (5–10 cm in diameter), with rough, corky bark, and a tuft of long, narrow, tough leaves at the crown. Once the tree has flowered, it branches and produces multiple heads of leaves. Trees can grow up to 15–20 m tall, with massive trunks to 1.5 m in diameter. Trees in the wild are generally shorter and stouter the further south and higher in altitude they grow.

The leaves are erect, but bend and drop after 2 years' growth. On younger trees the dead leaves hang down and form a thick skirt around the trunk. This is particularly noticeable in trees growing at higher latitudes and appears to protect the tree from cold as well as providing a genial home for insects such as the cabbage tree moth. Tī growing in northern regions drop dead leaves much faster.

The leaves vary in width and length and there are several recognisable forms. Trees with narrow leaves, tī kouka tarariki, are found from East Cape to Wairarapa, and were favoured for their strong fibre. Tī kouka wharanui are found in the west and south and have longer, broader, softer leaves. In western Northland and Auckland, there is a form called ‘tītī’, generally more spindly with short, broad leaves. In the central North Island are tī manu, tall trees with stout stems and large, broad, stiff leaves. Details on these variations can be found in Philip Simpson’s book on cabbage trees, Dancing Leaves (see references).

The large flowering heads herald spring’s arrival with their sweet scent. The flowering spike has a myriad of tiny branches bearing five to ten thousand minute, white to pinkish brown flowers, which open sequentially. After 2 months or so, the little fruits form (4–5 mm in diameter), changing from green through cream to cream/blue as they ripen. The substantial branches can easily bear the weight of a kererū, but today it is more likely to be starlings and blackbirds that eat and spread the fruit.

Pests and diseases

An annoying pest for weavers is the caterpillar of the cabbage tree moth, Epiphryne verriculata. The moth is nocturnal, and hides during the day on the underside of dead leaves. The brown-yellow lines that run across the body and wings provide a brilliant camouflage. Eggs are laid on both the dead and green leaves, and newly hatched caterpillars head for the green growing shoots (rito). They eat the leaf surface, the margins, and often destroy the heart of the rito.

The caterpillars of the moth Catamacta lotinana draw the leaf margins together with silk and pupate inside. When they emerge, the leaf looks shredded.

Scale insects, Leucapsis cordylinidis, can be found in large quantities on the underside of the leaves, where they suck the sap and allow the introduction of fungal diseases.

Sudden decline

The most lethal of diseases to affect cabbage trees is sudden decline, which causes the leaves to yellow, wilt and fall off. The tree dies, usually within a few weeks or months. An epidemic in the 1990s killed huge numbers of trees, particularly in northern New Zealand.

Sudden decline causes the leaves to yellow. Image - R.E. Beever
 ... wilt and fall off...Image - R.E.Beever
 and the tree to die. Image - R.E. Beever

Sudden decline causes the leaves to yellow,

... wilt and fall off...

 and the tree to die.
Images - R.E. Beever
 

A minute specialised bacterium, Phytoplasma australiense, is responsible. This phytoplasma is native to harakeke, where it causes the disease yellow-leaf.

Propagation

Tī kōuka are easily grown from seed and seedlings often appear in the garden if there is a tree nearby. Tī are very hardy and will grow happily in most soils, but will not withstand long periods of drought.

Further reading

Simpson P 2000. Dancing leaves. The story of New Zealand’s cabbage tree, tī kōuka. Christchurch, Canterbury University Press.

 

Prepared by Sue Scheele