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Once the sole genus in the family Casuarinaceae, as of 2010 some of the species that were previously part of Casuarina are now distributed into three other genera. The 17 species that now make up this genus range from large evergreen shrubs that measure 10 feet (3 m) to trees that can grow up to 115 feet (35 m) tall. This genus’ name, Casuarina, comes from the Malay word kasuari, referring to the cassowary owing to the similarities between these plants’ foliage with the bird’s feathers. The common names she-oak, ironwood, and beefwood are used to refer to these species. Native to Asia, Australia, and the Pacific Islands, these plants are now also found in the Americas and Africa.
In general, these plants have leaves that are tiny and tooth-like, forming rings around modified branchlets, which are usually mistaken for its leaves. During the winter, they bloom with discreet reddish flowers. Their fruit are hard, woody, and cylindrical cones that attract birds like parrots and cockatoos that eat the seed heads, as well as the moths and beetles that feast on the fruit. Some species produce an edible resin that is used as a food source by Aborigines.
Casuarina plants have a wide latitude in their soil demands. They can grow not just in dry and salty soils on the seashore, but also on rocky or volcanic soils in the mountains. Even if they prefer well-drained soils, they can also survive in wet or calcareous soils. These plants have minimal water needs and can withstand periods of drought.
One notable characteristic of Casuarina plants are their negative allelophatic properties, as evidenced by the typical absence of understory around them. It has been observed that once they dominate a site, their heavy root mat and the fallen litter at their base inhibit other plants from growing. The species C. equisetifolia in particular, referred to as Australian pine in Florida, has been declared invasive and is included in the U.S. Federal and State Noxious Weed list due to this. Authorities have deemed that it is a threat to many endangered plant species in the Everglades National Park.
In contrast, this characteristic is valued in its native Australia, where it is called the Aboriginal woman’s tree. As virtually no other plants can grow underneath, Aboriginal children are known to be found playing underneath these trees, as they are believed to be in no danger from the "bush devil” or snakes, as these avoid the fallen litter of branchlets and leaves. Commercial uses of Casuarina plants include using it in landscaping as hedges and to stabilize the soil near drainage and shores. As it can survive in windswept locations, they are widely planted as windbreaks. The wood is also harvested for fencing, shingles, and firewood.