Australia Geography: Flora

Australia's characteristic vegetation began to take shape about 55 million years ago when Australia broke from the super continent of Gondwanaland. At this time, Australia was completely covered by cool-climate rainforest, but as the continent drifted towards warmer climes, it gradually dried out, the rainforests retreated, plants like eucalypts and wattles (acacias) took over and grasslands expanded, resulting in the distinctive habitats found today.

Despite vast tracts of dry and barren land, much of Australia is well vegetated. Forests cover 5%. or 410,000 sq km. Plants can be found even in the arid centre, though many of them grow and flower erratically.

The arrival of Europeans 200 years ago saw the introduction of new flora, fauna and tools. Rainforests were logged, new crops and pasture grasses spread, hoofed animals such as cows, sheep and goats damaged the soil, and watercourses were altered. Irrigation, combined with excessive tree clearing, gradually resulted in salination of the soil. Human activities seriously threaten Australian flora but to date most species have survived.

There are more than 700 native Australian grasses found in a variety of habitats across the country.

Millions of sheep and cattle living in the arid zone owe their survival to dry shrubby plants called saltbush, named for their tolerance to saline conditions. Saltbush is extremely widespread and can be dominant over vast areas. There are 30 different species.

The most well-known of Australia's 40 palm species is the cabbage palm (Livistona mariae) of Palm Valley in the Finke Gorge National Park near Alice Springs. The tree grows up to 30 meters high, and is unique to this area. The growing tip of the tree consists of tender green leaves, and these were a source of bush tucker to Aboriginal people. The mature leaves were also woven into hats by early European inhabitants of the Centre.

The Australian species of the genus Acacia are commonly known as wattle and they are common indeed, with over 660 species known to exist in Australia. They vary from small shrubs to towering blackwoods.

Most species flower during late winter and spring. At this time the countryside is often ablaze with yellow flowers, and it's easy to see why a wattle is Australia's floral emblem.

The largest of the acacias, the blackwood (A. melanoxy-lon) can more meters high in good soil and is generally found on the ranges of eastern and southern Australia.

The mulga (A. is the dominant species in huge areas of inland Australia. It is very drought tolerant, and the hard wood was preferred by Aboriginal people for making spears and other implements.

The golden wattle (A. pycnantha) is Australia's floral emblem, and is one of the most widespread acacias. It grows best in hot and arid areas, but is common throughout south-eastern Australia.

The eucalypt (Eucalyptus spp), or gum tree, is ubiquitous in Australia except in the deepest rainforests and the most arid regions. Of the 700 species of the genus eucalyptus, 95% occur naturally in Australia, the rest in New Guinea, the Philippines and Indonesia.

Gum trees vary in form and height from the tall, straight hardwoods such as jarrah, karri and mountain ash to the stunted, twisted, shrub-like Mallee gum.

River Bed Gums (E. camaldulensis) are generally confined to watercourses where their roots have access to a reliable water source. They are massive trees which can grow up to 40 meters high and can live for up to 1000 years.

The boab (Adansonia gregorii) is Australia's most grotesque tree and is found only from the south-western Kimberley to the Northern Territory's Victoria River, where it grows on flood plains and rocky areas. Its huge, grey, swollen trunk topped by a mass of contorted branches makes it a fascinating sight, particularly during the dry season when it loses its leaves and becomes 'the tree that God planted upside- down'. Although boabs rarely grow higher than 20 meters, their moisture-storing trunks can be over 25 meters in girth.