Australia is a country of great beauty renowned for its unique animal species and rich, abundance of flora and fauna. The broad range of habitats varying from vast desert wilderness known as “The Outback” to urban cityscapes, ensures that Australian native plants have distinctively adapted to the great variability in habitats.
However, Australia’s subtropical climate and substantial variability in environmental conditions continues to be a significant threat to biodiversity in both endemic native plants such as Buckinghamia Celsissima and Grevillea Banksii and markedly in introduced exotic species such as Hibiscus Rosa-Sinensis.
Both native Australian plants Buckinghamia Celsissima and Grevillea Banksii are part of the Myrtaceae genus, comprising a vast assemblage of plants estimated include over 5950 species exclusively adapted to the harsh, intermittent Australian conditions, thus its capacity to endure solidity in these conditions. The environmental factors of sunlight, flood and fire can easily discern the differences between native Australian plants from exotic plants in their adaptability to Australia.
Buckinghamia Celsissima is native to Queensland rainforest habitats in North Eastern Australia. Similarly, Grevillea Banksii is native to Central Eastern Australia. Both of sup-tropical and temperate areas which frequently experience extreme heat and strong sun. Both native plants prefer full or partial sunlight, although they are also shade tolerant and thrive in high humidity tropical conditions, with an inclination to grow in the direction of sunlight.
Tolerance of Australian weather fluctuating from below zero temperatures to intolerable heat is essential to their survival and have therefore adapted to accommodate to numerous diverse environmental conditions. Due to the strong, constant sun throughout all seasons in Australia both Buckinghamia Celsissima and Grevillea Banksii have adapted to grow more leaves in shady areas in order absorb maximum light to convert as much energy into food as possible with a low rate of cuticular transpiration and reduction in leaf area to lessen extensive exposure to sunlight, as demonstrated in figure 1.
Comparatively, Hibiscus Rosa-Sinensis is native to South-East Asia, China, and is widespread in cultivation throughout tropical Asia.
Consonantly, Hibiscus Rosa-Sinensis also requires full sun, although excessive sunlight may cause the flower to wilt and tends to droop facing away from the sun. Whilst the temperatures in Australia and Asia may seem similar, Australia’s sun is far more severe and can be damaging to the flower.
The Hibiscus Rosa- Sinensis’ native environment is warm and humid hence its moist deep green, lush foliage and flamboyantly coloured petals which un-ideally absorb heat. Alternatively, Australia’s hot, dry, climate requires attributes which complement the inimitable environment conditions.
This is exemplified by the native plants which have lighter green to grey leaf colours to reduce heat absorption, waxy leaf surface and thin spines on leaves, hence the greater suitability to Australian environmental conditions.
Australia’s hot, dry climate is extremely prone to bushfire, Buckinghamia Celsissima and Grevillea Banksii, are both native to areas where bushfires are very common and widespread. Over time the native plants have adapted to have thick bark which protects the sensitive living tissues from weather and predation.
Thick bark protects the trunk as it is highly susceptible to fire, does not catch fire or burn easily. The capacity to sprout new growth, with deep roots of up to 15 meters deep allows access to stored ground water when the fire-scorched surface is dry. (Washington Native Plant Society, 2015)
This is illustrated by figure 2 which depicts the fire resistance of the thick bark by insulating and protecting inner tissue from excessive damaging heat. Comparatively, Hibiscus Rosa- Sinensis has vegetative insulation on leaf base which protects roots from heat and damage, allowing seeds to then readily re-sprout after fire. Both the native and exotic species have protective mechanisms which assist in survival during periods of fire.
However, natives have significant leverage as they are drought tolerant plants which encompasses a great succor in survival during extreme heat and drought during bushfires.
Australia is generally dry, however in the happening of a flood it is usually result of breaking drought. In both native species, excess water can effectively kill the plants as the inundation of soil prevents oxygen and carbon, both of which being essential for survival.
The excessive moisture in soil decreases oxygen levels impeding respiration in the roots leading to a build-up of carbon dioxide, methane and nitrogen gases which suffocates roots causing them to die. The depletion of available oxygen in soil and prevents the transport of minerals and nutrients in roots.
The native plants have adapted to flood by regulating transpiration, the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapour and is released to the atmosphere (Water Science School, 2016) thus ensuring no excess of water can drown the plant.
Similarly, water stress is detrimental to Hibiscus Rosa Sinensis and too regulates transpiration to evade flood damage however Hibiscus Rosa Sinensis achieves this by the Stomata pores in the epidermis of leaves and stems, whilst this is effective in moderating excess water, the sunken in pits and grooves can become waterlogged hence its lack of effectiveness in a flash flood circumstance which frequently occur in Australia.
Australia’s vast, harsh conditions of are not of ideal growing conditions for any plant. However, Australian natives, Buckinghamia Celsissima and Grevillea Banksii of the Myrtaceae genus have exceptionally adapted to the erratic Australian environment conditions and prospered.
On the contrary, whilst the Hibiscus rosa-sinensis is a striking, remarkable flower, that complements perfectly the picturesque Australian wildlife, it is not compatible with the Australian environment as it is clearly not accustomed to such conditions. A distinct trend in the adaptations of native and exotic plants is that the native plants such as Buckinghamia Celsissima and Grevillea Banksii tend to avert undesirable environmental conditions whilst exotics plants such as Hibiscus Rosa-Sinensis tend to attempt at coping with these conditions.