Answer: Casuarina, also called Beefwood or She-Oak, is considered an invasive alien, and is therefore not readily available in nurseries.
Here's the description of the threat it poses;
A member of the beefwood family (Casuarinaceae), Australian pine is a deciduous tree with a soft, wispy, pine-like appearance that can grow to 100 feet or more in height.
Also known as ironwood, beefwood, she oak and horsetail tree, it bears a superficial resemblance to the conifer genus Pinus because of its small, round, cone-like fruits and its branchlets of scale-like leaves that look like pine needles. Its flowers are tiny, brown and wind-pollinated. The fruit is a nutlet about ? inch in diameter that contains winged seeds.
ECOLOGICAL THREAT: Australian pine is fast-growing (5-10 feet per year), produces dense shade and a thick blanket of leaves and hard, pointed fruits, that completely covers the ground beneath it. Dense thickets of Australian pine displace native vegetation. Because its roots are capable of producing nitrogen through microbial associations, Australian pine can colonize nutrient-poor soils. Once established, it radically alters the light, temperature, and soil chemistry regimes of beach habitats, as it outcompetes and displaces native plant species and destroys habitat for native insects and other wildlife. Chemicals in the leaves of Australian pine may inhibit the growth of other plants underneath it.
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