The diverse flora of the Australasian tropical bush...
This is one of the biggest of all families of plants, with up to 35,000 species. Most tropical orchids are epiphytic (growing on other plants), with some being lithophytic (growing on rocks). The flowers of orchids are famous because they have varied colours, elaborate patterns and bizarre shapes. Part of their unusual shape is due to the uneven petal arrangement, which is known as zygomorphic, and there is frequently a twisting and elongation of the sepals and petals. The unusual flowers of many species have evolved specifically with particular species of insects, most commonly wasps. If pollinated, the flowers are followed by small, hard fruits that release lots of tiny seeds.
There are about 50 species in this genus, and they are found throughout tropical Asia and the islands of the south-west Pacific. They were recently split from Dendrobium. The plants are usually made up of large stalks with thick leaves. They are generally long lived and hardy for an orchid, and thus include some species that can handle and grow on the exposed salty edge of coastal habitats. The flowers are frequently large and colourful, and often have wavy or twisted petals. The flowers also live longer than most orchid flowers, and are mostly pollinated by large wasps.
Durabaculum undulatum (previously Dendrobium discolor) 'Golden Antelope Orchid'. Epiphytic, including in mangrove trees, but more commonly growing as a lithophyte (including on seashore rocks). Large sprays of colourful flowers growing on long woody stalks. Stems may stretch out for a metre. Flowers vary in colour depending on variety, but usually gold. Grows in rainforest, mangroves, open forest, mainly in coastal situations, from central Queensland Australia up into New Guinea. Because of its hardiness, is popular in tropical gardens.
There is only 1 genus in this family.
Flagellaria indica ‘SuppleJack’, ‘Whip Vine’. One of the fastest growing climbers along the Australian coast. Unusual modified tendril-tipped leaves. White flowers produced at end of stem. Found growing over vegetation in mangroves, monsoon and rainforest along the tropical Australian coast, and up into tropical Asia. Can also be found climbing over boulders on tropical Australian beaches.
There are only 4 species in this genus, and they are restricted to the Old World tropics of Africa, Asia and Australia. They are generally fast and vigorous climbers with round, cane-like stems and long leaves. These long leaves are unusual as the tips have been modified into tendrils to enable the plant to curl its way through the canopy. They are found on trees in various tropical habitats.
The family Passifloraceae includes over 600 species, found mainly through the tropics of the world. They grow as trees and shrubs, but are most famous as vines. The leaves of most common species in this family are usually heart-shaped or lobed, and often have two glands at the base. A winding tendril is used to climb, and this sprouts from a bud at the base of the alternate leaves, a distinctive feature of the family. The flowers are both striking and unique, due to the many frilled ring. The fruits contain many seeds, which are surrounded by a pulpy aril.
There are over 370 species of passionfruit vines and they are found in the tropical Americas, Asia and the Pacific. The flowers have the distinctive ring of frills indicative of this family, Three long styles that ride atop the central stalk, and 5 drooping stamens slightly below and from the same central stalk. These distinctive and elaborate flowers were named by Spanish missionaries for the passion of Christ; the stigma and anthers representing the nails and the wounds, and the frills representing the crown of thorns (Hutton and Cassio 1996). There are several native and introduced species in Australia.
Passiflora foetida, ’Stinking Passionfruit’. One of the most common passionfruit species in tropical Australia. The leaves usually have 3 main lobes. The stems are hairy. As suggested by the name, they smell when crushed. Flowers and fruits in the dry season. Beautiful white flowers that open at night, and may seen early the next morning. Pale green spiky looking bracts beneath the flower contain the growing fruit in a ‘cage’. Fruit ripens from green to orange. Ripe fruit is edible, but rest of plant and unripe fruit are toxic. Native to South and Central America, introduced into Australia over a century ago. Also found throughout the tropics of the world.
Large bright yellow flower followed by large baseball fruits full of soft hairs that wind distribute the seeds.
Cochlospermum gillivraei, 'Kapok'. Found in the tropical woodlands of north-east Queensland, and into Northern Territory and New Guinea; seems especially common on the slopes of hills.
Brachychiton rupetris, 'Queensland Bottle Tree'. Swollen trunk. Leafless in winter.
The family Myrtaceae is arguably the most important on the Australian continent, and are common and dominant in the woodlands.
The most useful diagnostic feature of this family are the leaves and their obvious oil glands, which may appear as light dots when the leaves of certain species are held up against bright light. The flowers in the Myrtaceae family are usually quite showy, but not in the usual way; instead of colourful petals, there is instead a seemingly unlimited number of stamens, giving the flower the appearance of a brush.
Botanists often divide the family into two different sub-families. One group are the ‘woody-fruited myrtles’. These are dominant in drier parts of our continent, and include the classic Australian genera such as Eucalyptus, Melaleuca and Callistemon, and are common in the woodlands just behind the coast along most of Australia. The other group, the ‘soft-fruited myrtles’ are usually associated with wetter environments and found mainly in the tropical rainforests.
Xanthostemon, 'Golden Penda'. Large yellow flowers. The genus name means 'yellow stamen'. These plants grow in rainforest and woodlands across northern Australia, New Guinea, across to New Guinea and north into Philippines.
Nepenthes, 'Pitcher Plant'. Carnivorous climber.
Scheflera actinophylla, 'Australian Umbrella/Octopus Tree', (Lizard Island, Australia). Found mainly in rainforest, but also more open habitats, in North Queensland, Northern Territory, and New Guinea.