Belonging to the Casuarina genus, Casuarina equisetifolia is a she-oak species.
They are also known as Australian pine, beefwood, ironwood, and horsetail tree. Some of the Casuarina species belonging to this genus are Casuarina glauca, Casuarina oligodon, Casuarina junghuhniana, Casuarina cristata Miq, and many others.
Casuarina is a deciduous tree that can grow up to 115 ft (35 m), has a pine-like appearance, and is mainly found in coastal habitats, such as estuaries and beaches. Its leaves resemble pine needles and the fruit has a conical shape even though it is not an actual conifer. This cone-like fruit that contains winged seeds has a diameter of 0.5 in (1.27 cm). The flowers are brown in color, small in size, and wind-pollinated in nature.
These invasive species of plants are really detrimental to certain animals and vegetation. A Casuarina tree can possess chemicals in its different body parts, including seeds and leaves. These chemicals are powerful enough to prevent the development and growth of competing trees and at last, displace them altogether.
Where do Casuarina trees grow?
Casuarina trees are salt-tolerant, therefore they can be seen in exposed sand bars, sandy flats, foreshore dunes, and rocky strands. Also, they are well adapted to sustain in any habitat.
- The native range of Casuarina is limited to the tropical and subtropical seacoast, mainly from Malaysia to Australia, Melanesia, Micronesia, Polynesia, and the Philippine Islands.
- The non-native range includes Florida, Hawaii, the Bahamas, Puerto Rico, and many other islands of the Caribbean where this tree was introduced later. Today, they can be found on frost-free coastlines nearly everywhere in the world.
- Casuarina trees can sustain in a wide range of soil types, but they prefer coarse-textured soils like highly saline and dry soils of sea beaches.
- They also prefer the soils that have developed on weathered volcanic flows and that are young and nutrient-poor.
- Casuarina trees can tolerate extremely salty soil and salt spray that can be found on windward beaches.
- These trees are known for growing fast in hot weather, and they can endure annual temperatures as high as 86 °F (30 °C).
- They also have some enemies like predatory insects, due to the high tannin content of their saplings and foliage.
- The Australian pine, like some other species of the Casuarina genus, is an actinorhizal plant and has the ability to fix atmospheric nitrogen.
Uses Of Casuarina Trees
Even though their flowers and fruits are inedible and are of no use to us, these plants can be used by humans for other purposes.
- Casuarina is one of the most popular names in the world of bonsai. In some parts of the Caribbean and Southeast Asia, these trees are a bonsai subject. The plants cultivated in Taiwan and Indonesia are regarded among the best in the world.
- Casuarina is known for producing firewood of excellent quality. Also, the wood can be used for fencing and shingles.
- In the urban regions, the leaves of these plants are used for ornamental purposes.
- It is discovered that Casuarina leaves and bark can be used for removing textile dyes. While the leaves are effective on methylene blue, reactive orange 16 Rhodamine B, methyl violet 2b, and malachite green, the Casuarina bark is only effective on methylene blue.
- Casuarina seeds can also be used to remove textile dyes such as malachite green and neutral red.
- For treating cancer, inflammation, and other diseases, Casuarina equisetifolia Lin. has been traditionally used. Though the bark is said to have done some anti-arthritic activities, its efficacy in treating arthritis has not been scientifically examined.
Disadvantages Of Casuarina Trees
The Australian pine is known for changing habitat, growing rapidly, out-competing and destroying native species, and contributing to soil erosion.
- The Casuarina trees form a dense forest after colonizing an area and make it impossible for any other species to grow and survive there. They form impenetrable thickets that block a significant amount of sunlight from reaching the ground.
- This invasive species does everything possible to displace the native tropical plant species who are well adapted to mangrove swamps, beaches, and other coastal environments.
- It is said that Casuarinas eliminate competing plant species by using allelopathy, which is the act of releasing some chemicals that prevent the development and growth of competing plants.
- This statement is corroborated by the mere absence of any other plant species near or under the dense thickets of Casuarina.
- The chemicals used in the allelopathy process are either phenols or terpenes. Large quantities of these chemicals are present in the stems, roots, leaves, seeds, or fruits of the trees of this invasive species.
- Casuarina trees are known for lowering the water table of an area and exhausting the moisture in the soil. By displacing deep-rooted vegetation they also facilitate beach erosion.
- Due to their shallow root, Casuarinas tend to topple and uproot during high winds, which can cause significant damage to coastal storm evacuation routes. For the same reason, a Casuarina-filled beach is prone to erosion and sand loss.
- By ruining native beach vegetation that is home to many animals, Casuarina is putting their lives in danger. This tree is already threatening some endangered animal species like the American crocodile, the green turtle, and the loggerhead turtle.
- Not only to animals and vegetation, but Casuarinas can cause much damage to humans too. With their tall canopies and shallow roots, they become the real danger during high winds and storms.
- There are many ways in which you can prevent this invasive species from damaging others. Some of them are the Australian defoliating moth, the Floridian root rot, and a host-specific seed-feeding wasp.
What fruit does a casuarina tree produce?
Casuarina fruits are tiny, oval, and resemble the fruits of coniferous trees.
- The fruits of Casuarina trees have an oval structure with a length of 0.39-0.94 in (10-24 mm) and a diameter of 0.35-0.51 in (9-13 mm).
- These fruits superficially resemble a conifer cone and are made up of multiple carpels. Each of these carpels contains a seed with a small wing that is 0.24-0.31 in (6-8 mm) in length.
- These fruits are often used to remove textile dyes of various colors.
- Apart from that, Casuarina is also a flowering plant and produces both male and female flowers in small inflorescences. While the male flowers look like pine needles and grow at the twig tips, the female flowers are brown-red in color and grow on short peduncles.
- Most trees in the US blossom twice a year from September to October and February to April.
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