CASUARINA, a genus of odd trees containing about 35 species, chiefly Australian, but a few Indo-Malayan. The long whip-like green branches are longitudinally grooved, and bear at the nodes whorls of small scale-leaves, the shoots resembling those of Equisetum (horse-tail). The flowers are unisexual. The staminate are borne in spikes, each flower consisting of a central stamen which is surrounded by two scale-like perianth-leaves. The pistillate are borne in dense spherical heads; each flower stands in the axil of a bract and consists of two united carpels flanked by a pair of bracteoles; the long styles hang out beyond the bracts, and the one-chambered ovary contains two ovules. In the fruit the bracteoles form two woody valves between which is a nut; the aggregate of fruits resemble small cones. Pollen is transferred by the wind to the long styles. The pollen-tube does not penetrate the ovule through the micropyle but enters at the opposite end—the chalaza (see ANGIOSPERMS).
The wood is very hard, and several species are valuable timber trees. From a fancied resemblance of the wood to that of the oak these trees are known as "oaks," and the same species has different names in different parts such as "she-oak," "swamp-oak," "iron-wood" and "beef-wood." Several species are cultivated in the subtropical parts of the United States, especially the beef wood (C. equisetifolia), which has become naturalized in Florida. See J. H. Maiden, Useful Native Plants of Australia (London and Sydney, 1889).