Plants of the Kakadu region Kakadu's flora is among the richest in northern Australia-more than 1700 plant species are recorded. This richness is a result of the Park's geological, landform and habitat diversity. Kakadu is also considered to be one of the most weed free national parks in the world — only 5.7 per cent of recorded species are weeds (Press et al 1995). The 1995 edition of Rare and Threatened Australian Plants (Briggs & Leigh 1995) identifies ninety-seven rare, vulnerable or poorly known plant species that occur in Kakadu. The stone country and outliers

The stone country Plants growing in the stone country and on the outliers must survive extremely hot, waterless conditions for many months each year. Among the best examples of plants well adapted to these harsh conditions are the resurrection grasses, which dehydrate in the absence of moisture and spring back to life within twentyfour hours of rain. Monsoon forests often develop in the cool, moist gorges that dissect the stone country. They are generally dominated by Allosyncarpia ternata, a large, spreading, shady tree restricted to the Kakadu and Arnhemland plateau. More widespread and easily recognisable stone country and outlier plants are spinifex and the sandstone pandanus; both can be found at Nawurlandja. The southern hills and basins The habitats of the southern hills and basins support several endemic plantsplants not found anywhere else in the world. One example is the untidy Eucalyptus koolpinensis, known from only two populations near Jarrangbarnmi (Koolpin Gorge). Perhaps the most noticeable plant in the woodlands of the south of the Park is the salmon gum (Eucalyptus tintinnans). When this tree sheds its old white bark it exposes a beautiful salmon-coloured bark, which gradually fades to white and is shed the following year.

The lowlands The greater part of Kakadu is covered by eucalypt-dominated open forest and woodland. These tracts are among the last expanses of virgin eucalypt forest in Australia. The lowland plants are heavily influenced by seasonal factors. The wet season is a period of growth, when plants make the most of the abundant water. The dry season is a more stressful time, and the plants have a variety of mechanisms for coping with this long waterless period. Some, such as the kapok bush, are deciduous. Others, such as the green plum, are semi-deciduous and

have a waxy film on their leaves to help reduce water loss. Eucalypts generally have a deep root system, enabling them to reach the available ground water. The lowlands are a mosaic of vegetation communities. Local differences in slope, soil composition and the flooding regime combine to favour either open forest, woodland or grassland.

Nymphoides indica Open forest is dominated by the Darwin stringybark, Darwin woollybutt and Cooktown ironwood. Late in the dry season the Cooktown ironwood, with its dark, chunky bark and lime-green leaves, stands out from the surrounding vegetation. Woodlands contain many types of eucalypts, including bloodwoods and boxes. The understorey of both open forest and woodland is generally made up of smaller trees such as pandanus and green plums, shrubs, and tall grasses such as spear grass. The greatest species diversity occurs, however, in the ground layer, where there is a large range of grasses, sedges and wildflowers. The floodplains Where floodplains are inundated for two to six months a year grasses and sedges such as spike rush occur. Clumps of freshwater mangroves (itchy tree), pandanus and paperbarks are found on slightly higher ground. Herbaceous swamp vegetation dominates areas covered by water for six to nine months a year. A variety of waterlilies, such as the blue, yellow and white snowflake, are commonly found in these areas.

Floodplains Tall, dense stands of paperbark trees grow on the margins of Magela Creek, Yellow Water, Anbangbang Billabong and other floodplains and permanent waterholes. The dominant species are the broad-leafed and weeping paperbarks. Freshwater mangroves and water pandanus are also common. The estuaries and tidal flats Mangroves are common along the banks of tidal creeks and rivers. Thirty-nine of the forty-seven Northern Territory species of mangrove occur in Kakadu. Mangroves are important for stabilising the coastline and serve as feeding and breeding grounds for many animals, including fish such as barramundi.

Mangroves Like other plants growing in estuaries and tidal flats, mangroves must be able to cope with oxygen-deficient soils and periodic inundation by salt water. Mangroves use a range of mechanisms to cope with these conditions. Some species, such as the grey mangrove, have roots projecting through the soil (pneumatophores); others, such as the spider mangrove, have an amazing raised root system-like the legs of a spider-to help with oxygen intake. A number of mangroves are able to exclude salt through specialised filters in their roots or through salt glands in their leaves. On the tidal flats behind the mangroves, hardy succulents (samphire), grasses and sedges grow. Isolated pockets of monsoon forest grow along the coast and river banks. These forests contain several impressive trees, among them the banyan fig, which can be recognised by its large, spreading aerial roots, and the kapok tree, which has a spiny trunk, large, waxy red flowers and pods full of cotton-like material. Plants that are common in Kakadu

Grevillea pteridifolia A number of publications describe Kakadu's flora: John Brock's Native Plants of Northern Australia and Kym Brennan's Wildflowers of Kakadu are examples. Following is a summary of some of the plants often seen in Kakadu. The descriptions are taken from the work of Brock and Brennan. The name in bold type is the plant's common name, then name in italics is its scientific name and the underlined name is its Gun-djehmi name. The Sandstone Country Allosyncarpia Allosyncarpia ternata An-binik — is a large, hardy evergreen that is restricted to the stone country of Kakadu and Arnhemland. Native ginger Curcuma australasica — is an attractive leafy annual that grows from a tuber. Its hot pink flowers can be seen at Ubirr and Nourlangie in the wet season. It is also related to the turmeric plant, a native of Asia.

Cochlospermum fraseri Pityrodia jamesii — is a shrub that grows on rocky areas in pockets of sandy soil. Pink-white flowers appear in September to December. The shrub's sticky, fragrant leaves are the main food of Leichhardt's grasshopper. Sandstone pandanus Pandanus basedowii An-more — grows only in the sandstone areas of Kakadu and Arnhem Land. The Lowlands

Billy goat plum Terminalia ferdinandiana An-morlak — is harvested commercially outside of Kakadu and marketed as the Kakadu plum. It is a medium-sized tree with large broad leaves. It is deciduous in the dry season and between March and June and bears edible fruits known to have exceptionally high levels of vitamin C. Cooktown ironwood Erythrophleum chlorostachys An-dubang — is a tall, spreading tree with distinctive rounded dark-green leaves. Late in the dry season it puts out new leaves that are a bright lime-green. The tree's timber is extremely hard and termite resistant. All parts of the tree are highly poisonous to mammals.

Brachychiton paradoxum Darwin woollybutt Eucalyptus miniata An-djalen — grows to 10-20 m; it has dark, rough bark on the lower half of its trunk and smooth, white bark on the upper half. Bright-orange flowers appear between May and August. Fern-leafed grevillea Grevillea pteridifolia An-dadjek — is a medium-sized slender tree with long, narrow silver foliage. The flowers are bright orange and appear from May to August. The nectar from the flowers attracts many birds. Green plum Buchanania obovata An-dudjmi — is a medium-sized tree with large, thick leathery leaves. Bunches of green grape-sized plums appear in October to December; they are considered to be some of the best bush tucker around. Kapok bush Cochloprerum fraseri An-djedj — is deciduous in the dry season, from May to August, and has distinctive bright-yellow flowers. Its large, fragile pods are filled with a dense, soft cotton-like material.

Pandanus spiralis The red-flowered kurrajong Brachychiton paradoxum An-marrenarnak — is a small, often straggly tree that is widespread on the lowlands. It is deciduous in the dry season, when bright-red bell-shaped flowers appear on short stems from the branches. Sand palm Livistonia humilis An-gulalurrudj — is a slender fan palm with small yellow flowers on long spikes. Aboriginal people use it for medicines, fibre, dye and food. Spear grass Sorghum spp. An-ngulubu — grows to over 2 metres and becomes the dominant understorey plant towards the end of the wet season. Spiral pandanus Pandanus spiralis An-yakngarra — grows in a broad range of habitats, often in dense stands. Aboriginal people use it for medicines, fibre and food.

Banksia dentata The swamp banksia Banksia dentata Guibuk — is the only banksia found in the Top End. It has distinctive serrated leaves and the characteristic banksia flower, which appears between January and April. Turkey bush Calytrix exstipulata Anbarndarr — is common throughout the lowlands. It bears masses of pink-purple flowers between May and August. The Rivers The freshwater mangrove Barringtonia actuangula An-galnggi — is a small, spreading tree that grows on the banks of freshwater creeks, rivers and swamps. It develops hanging, bright-red flowers between September and December. It is also known as the 'itchy tree': small caterpillars feed on the leaves during the wet season and cause localised skin irritation if touched.

Calytrix exstipulata Silver-leafed paperbark Melaleuca argentea Gun-god — is a large, spreading tree commonly seen along the waterways. Its pale-yellow flower spikes appear mainly between June and October and produce a sickly sweet fragrance that attracts many animals. Water pandanus Pandanus aquaticus An-djimjim — commonly grows along the banks of permanent freshwater streams. Its fruit is inedible. Yellow bladderwort Utricularia vulva - is a small orchid-like plant that grows along sandy creek banks. The Wetlands The blue lily Nymphaea violacea Barradjungga — is commonly seen along the margins of billabongs. Its violet-tipped white flowers appear between January and July. The seeds and stems can be eaten raw; the tuberous underground bulbs can be eaten after cooking.

Nymphaea violacea

The red lily Nelumbo nucifera Wurrmarninj — grows in lowland wetlands. Its leaves are very large and stand erect above the water. Large, fragrant deep-pink flowers appear between March and November. Coastal Monsoon Areas Banyan Ficus virens An-borndi — is a large spreading tree with aerial roots and large prop roots from the major branches. It is a strangler fig with edible fruits and makes a great shade tree. Beach hibiscus Hibiscus tiliaceus — is a small tree, 5 to 8 metres high, commonly found in monsoon pockets along the coast and river banks. It has a large yellow flower with a dark maroon centre.