Cordyline australis, commonly known as the cabbage tree, or by its Māori name of tī or tī kōuka, is a widely branched monocot tree endemic to New Zealand.
It grows up to tall with a stout trunk and sword-like leaves, which are clustered at the tips of the branches and can be up to long. With its tall, straight trunk and dense, rounded heads, the tree is a characteristic feature of the New Zealand landscape. It is common over a wide latitudinal range from the far north of the North Island to the south of the South Island. It grows in a broad range of habitats.
Māori used it as a source of food, particularly in the South Island, where it was cultivated in areas where other crops would not grow. It provided durable fibre for textiles. Hardy and fast growing, it is widely planted in New Zealand gardens, parks and streets, and numerous cultivars are available. It can also be found in large numbers in island restoration projects, such as Tiritiri Matangi Island, where it was among the first seedling trees to be planted.
It is also grown as an ornamental tree in higher latitude Northern Hemisphere countries with maritime climates, including parts of the upper West Coast of the United States, Canada and the British Isles, where its common names include Cornish palm, cabbage palm, Torbay palm and Torquay palm.
Description Cordyline australis grows up to tall with a stout trunk in diameter. The largest known tree, at Pākawau, Golden Bay / Mohua, was estimated to be 400 or 500 years old, and stood tall with a circumference of at the base. Before it flowers, it has a slender unbranched stem. The first flowers typically appear at 6 to 10 years old, in spring. The right conditions can reduce the first flowering age to 3 years (Havelock North, 2015 mast year). After the first flowering, it divides to form a much-branched crown with tufts of leaves at the tips of the branches. Each branch may fork after producing a flowering stem. The pale to dark grey bark is corky, persistent and fissured, and feels spongy to the touch.
The long narrow leaves are sword-shaped, erect, dark to light green, long and wide at the base, with numerous parallel veins. The leaves grow in crowded clusters at the ends of the branches, and may droop slightly at the tips and bend down from the bases when old. They are thick and have an indistinct midrib. The fine nerves are more or less equal and parallel. The upper and lower leaf surfaces are similar.
In spring and early summer, sweetly perfumed flowers are produced in large, dense panicles (flower spikes) long, bearing well-spaced to somewhat crowded, almost sessile to sessile flowers and axes. The flowers are crowded along the ultimate branches of the panicles. The bracts which protect the developing flowers often have a distinct pink tinge before the flowers open. In south Canterbury and North Otago the bracts are green.
The individual flowers are in diameter, the tepals are free almost to the base, and reflexed. The stamens are about the same length as the tepals. The stigmas are short and trifid. The fruit is a white berry in diameter which is greedily eaten by birds. The flowers have a "strong and sweet scent", and the nectar attracts great numbers of insects to the flowers.
Large, peg-like rhizomes, covered with soft, purplish bark, up to long in old plants, grow vertically down beneath the ground. They serve to anchor the plant and to store fructose in the form of fructan. When young, the rhizomes are mostly fleshy and are made up of thin-walled storage cells. They grow from a layer called the secondary thickening meristem.
Regional diversity
New Zealand's native Cordyline species are relics of an influx of tropical plants that arrived from the north 15 million years ago in the warm Miocene era. Because it has evolved in response to the local climate, geology and other factors, C. australis varies in appearance from place to place. This variation can alter the overall appearance of the tree, canopy shape and branch size, the relative shape and size of the leaves, and their colour and stiffness. There may also be invisible adaptations for resistance to disease or insect attack. Some of these regional provenances are different enough to have been named by North Island Māori: in the north, in the central uplands, in the east and in the west. In Northland, C. australis shows a great deal of genetic diversity—suggesting it is where old genetic lines have endured. Some trees in the far north have floppy, narrow leaves, which botanist Philip Simpson attributes to hybridisation with C. pumilio, the dwarf cabbage tree.
In eastern Northland, C. australis generally has narrow, straight dark green leaves, but some trees have much broader leaves than normal and may have hybridised with the Three Kings cabbage tree, C. obtecta, which grows at North Cape and on nearby islands. These obtecta-like characteristics appear in populations of C. australis along parts of the eastern coastline from the Karikari Peninsula to the Coromandel Peninsula. In western Northland and Auckland, a form often called grows. When young, are generally very spindly, and are common in young kauri forests. When growing in the open, can become massive trees with numerous, long thin branches and relatively short, broad leaves.
In the central Volcanic Plateau, cabbage trees are tall, with stout, relatively unbranched stems and large stiff straight leaves. Fine specimens are found along the upper Whanganui River. On old trees, the leaves tend to be relatively broad. The leaves radiate strongly, suggesting that tī manu is adapted to the cold winters of the upland central plateau. It may have originated in the open country created by lava, volcanic ash, and pumice. Trees of the tī manu type are also found in northern Taranaki, the King Country and the Bay of Plenty lowlands.
Tarariki are found in the east of the North Island from East Cape to the Wairarapa. Māori valued the narrow spiky leaves as a source of particularly tough, durable fibre. Tarariki's strong leaf fibres may be an adaptation to the region's hot, dry summers. In parts of the Wairarapa, the trees are particularly spiky, with stiff leaves and partially rolled leaf-blades. The trees near East Cape, by contrast, have leaves that hang laxly on the tree. In Hawke's Bay, some trees have greener, broader leaves, and this may be because of wharanui characteristics brought in across the main divide through the Manawatū Gorge.
Wharanui grow to the west of the North Island's main divide. They have long, broad flaccid leaves, which may be an adaptation to persistent westerly winds. The wharanui type occurs in Wellington, Horowhenua and Whanganui, and extends with some modifications to the southern Taranaki coast. In Taranaki, cabbage trees generally have a compact canopy with broad straight leaves. In the South Island, wharanui is the most common form, but it is variable. The typical form grows, with little variation, from Cape Campbell to the northern Catlins, and from the eastern coast to the foothills of the Southern Alps / Kā Tiritiri o te Moana. In Marlborough's Wairau Valley, cabbage trees tend to retain their old, dead leaves, lending them an untidy appearance. The climate there is an extreme one, with hot, dry summers and cold winters.
In north-west Nelson, there are three ecotypes defined by soil and exposure. Trees growing on limestone bluffs have stiff, blue-green leaves. On the river flats, the trees are tall with narrow, lax, dark green leaves, and an uneven canopy. They resemble the cabbage trees of the North Island's East Cape. Along the coast to the far west, the trees are robust with broad, bluish leaves. The latter two forms extend down the West Coast, with the lax-leaved forms growing in moist, fertile, sheltered river valleys while the bluish-leaved forms prefer rocky slopes exposed to the full force of the salt-laden coastal winds.
In Otago, cabbage trees gradually become less common towards the south until they come to an end in the northern Catlins. They reappear on the south coast at Waikawa, Southland, but they are not the wharanui type. Rather they are vigorous trees with broad, green leaves and broad canopies. Absent from much of Fiordland, it was probably introduced by Māori to the Chatham Islands at 44° 00′S and to Stewart Island / Rakiura at 46° 50′S. They extend along the coast towards Fiordland, and inland to the margins of some of the glacier-fed lakes. Very vigorous when they are young, these trees seem well adapted to the very cold winters of the south.
A study of seedlings grown from seed collected in 28 areas showed a north-south change in leaf shape and dimensions. Seedling leaves get longer and narrower southwards. Seedlings often have leaves with red-brown pigmentation which disappears in older plants, and this colouration becomes increasingly common towards the south. The changes in shape—leaves getting narrower and more robust from north to south and from lowland to montane—suggest adaptations to colder weather.
Taxonomy and names
Cordyline australis was collected in 1769 by Sir Joseph Banks and Dr Daniel Solander, naturalists on the Endeavour during Lieutenant James Cook's first voyage to the Pacific. The type locality is Queen Charlotte Sound / Tōtaranui. It was named Dracaena australis by Georg Forster who published it as entry 151 in his Florulae Insularum Australium Prodromus of 1786. It is sometimes still sold as a Dracaena, particularly for the house plant market in Northern Hemisphere countries. In 1833, Stephan Endlicher reassigned the species to the genus Cordyline.
The genus name Cordyline derives from an Ancient Greek word for a club (kordyle), a reference to the enlarged underground stems or rhizomes, while the species name australis is Latin for "southern". The common name cabbage tree is attributed by some sources to early settlers having used the young leaves as a substitute for cabbage. However, the name probably predates the settlement of New Zealand — Georg Forster, writing in his Voyage round the World of 1777 about the events of Friday, 23 April 1773, refers on page 114 to the discovery of a related species in Fiordland as "not the true cabbage palm" and says "the central shoot, when quite tender, tastes something like an almond's kernel, with a little of the flavour of cabbage." Forster may have been referring to the cabbage palmetto (Sabal palmetto) of Florida, which resembles the Cordyline somewhat, and was named for the cabbage-like appearance of its terminal bud.
Cordyline australis is the tallest of New Zealand's five native Cordyline species. Of these, the commonest are C. banksii, which has a slender, sweeping trunk, and C. indivisa, a handsome plant with a trunk up to tall bearing a massive head of broad leaves up to long. In the far north of New Zealand, C. australis can be distinguished by its larger heavily branched tree form, narrower leaves and smaller seeds from C. obtecta, the Three Kings cabbage tree, its closest relative. C. australis is rather variable, and forms from the northern offshore islands may be hybrids with C. obtecta. Hybrids with C. pumilio and C. banksii also occur often where the plants are in close vicinity, because they flower at about the same time and share the chromosome number 2n=38, with C. australis.