Pandanus tectorius is a species of Pandanus (screwpine) that is native to Malesia, Papuasia, eastern Australia, and the Pacific Islands. It grows in the coastal lowlands typically near the edge of the ocean. Common names in English include thatch screwpine, Tahitian screwpine, hala tree (pū hala in Hawaiian) and pandanus. The fruit is edible and sometimes known as hala fruit.
Description P. tectorius is a small tree that grows upright to reach 4–14 m (13–46 ft) in height. The single trunk is slender with brown ringed bark. It is spiny, grows to 4.5–11 m (15–35 ft) in width, and forks at a height of 4–8 metres (13–26 ft). It is supported by aerial roots (prop roots) that firmly anchors the tree to the ground. Roots sometimes grow along the branch, and they grow at wide angles in proportion to the trunk.
Leaves The leaves are usually 90–150 cm (3–5 ft) in length and 5–7 cm (2–2+3⁄4 in) in width. They possess saw-like margins. Some varieties have spines along the edges and ribs throughout the leaves. The leaves are spirally arranged at the end of the branches.
Flowers
Pandanus tectorius is dioecious, meaning male and female flowers are borne on separate trees, with very different male and female flowers. Male flowers are arranged in racemes and are small, fragrant, and short-lived, lasting only a single day. The flowers are grouped in 3 and gathered in large clusters surrounded by big, white bracts. these clusters are about 1 ft in length and are fragrant. Female flowers resemble pineapples. In Hawaiʻi the male flower is called hīnano and the bracts are used for making very fine mats (moena hīnano' or ʻahu hīnano).
Fruit The female P. tectorius trees produce a segmented, large fruit. Although not closely related, the fruit resembles a pineapple. The fruit of P. tectorius is either ovoid, ellipsoid, subglobose or globose with a diameter of 4–20 cm (1+1⁄2–7+3⁄4 in) and a length of 8–30 cm (3+1⁄4–11+3⁄4 in). The fruit is made up of 38–200 wedge-like phalanges, often referred to as keys or carpels, which have an outer fibrous husk and are 8 inches in length. There are roughly 40 to 80 keys in each fruit and the color of the fruit can be yellow, orange, or red with a green top. Phalanges contain two seeds on average, with a maximum of eight reported. The phalanges are buoyant, and the seeds within them can remain viable for many months while being transported by ocean currents.
Taxonomy Pandanus tectorius was first described by Sydney Parkinson in 1774. It is an angiosperm belonging to the genus Pandanus of the family Pandanaceae.
Distribution and habitat Pandanus tectorius grows natively from the Philippines through the Pacific Ocean to Hawaii. It is found in parts of Malesia (the Cocos (Keeling) Islands, Java, the Lesser Sunda Islands, the Maluku Islands and the Philippines), throughout Papuasia, and in most of the tropical Pacific.
In Australia, it is native to an area from Port Macquarie in New South Wales to northern Queensland. Both the US and the Hawaiian Islands recognize only one indigenous species, P. tectorius. Its exact native range is unknown due to extensive cultivation; it may be an early Polynesian introduction to many of the more isolated Pacific islands on which it occurs. These islands include Micronesia and Melanesia. In Hawaii, P. tectorius is found natively on all the main islands except Kahoʻolawe, and it is known to have predated human settlement, based on seed and pollen samples taken from Kauaʻi's Makauwahi Cave. Pandanus tectorius naturally grows in coastal regions, such as on mangrove margins and beaches, at elevations from sea level to 610 m (2,000 ft). It requires 1,500–4,000 mm (59–157 in) of annual rainfall and seasons will fluctuate from wet to dry. Pandanus tectorius is considered more drought tolerant than coconut trees. The trees have adapted to drought by reducing fruiting. Thatch Screwpine is well adapted to grow in the many soil types present on coasts, including quartz sand, coral sand, and peat, as well as in limestone and basalt. P. tectorius is salt and wind tolerant and favors slightly acidic to basic soil (pH of 6–10). The trees are strong and can typically withstand tropical storms. It prefers to grow in full sunlight, but grows well with 30-50% shade. It will not tolerate shade above 70%.
Ecology There are a wide range of natural enemies that pose a threat to P. tectorius such as parasites, pathogens, and herbivores. They attack the leaves, roots, stems, and growing points. The stick insect Megacrania batesii lives and feeds only on P. tectorius and two other Pandanus species. Pandanus tectorius in Australia is threatened by a sap-sucking insect, Jamella australiae, a species of the genus Jamella of the subfamily Flatinae, known as the Pandanus planthopper. It has caused much damage to plants on the northern coast of New South Wales, before making its way up the coast to Noosa and the Gold Coast in Queensland in the 1990s. Since then it has infested pandanus further north, killing about 80 per cent of the P. tectorius population to the south of Gladstone, Queensland, and has since reached Yeppoon on the Capricorn Coast, where P. tectorius plays an important part in preventing coastal erosion. A natural predator in the form of a wasp native to northern Queensland, Aphanomerus pusillus, has been introduced on Fraser Island and in Byfield National Park as one of methods used to combat the pest. Other methods used on Fraser Island including the injection of insecticide into the plant, stripping infested leaves away, and breeding new plants from local stock. The wasp can only be used in the warmer months on the island, as it does not thrive in the cooler climate of southern Queensland.
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