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Casuarinaceae are perennial shrubs or trees, evergreen, with jointed stem and branches and a whorl of slender branches at each joints or nodes; branchlets grooved, green in colour and resemble the pine-needles to some extent; branches and branchlets usually drooping. Leaves scale-like, whorled at each node, united at the base forming toothed sheath round the axis.
Flowers of Casuarinaceae are unisexual, very small and inconspicuous, in catkin-like inflorescences at the end of the branchlets; the male flowers are in several whorls on the catkin-like spike, each whorl in a sheath formed by the union of bracts; each flower is surrounded by a pair of bracteoles; the pistillate or female flowers are borne in a small capitates pike, each flower in the axil of a bract and subtended by a pair of bracteoles which enlarge and form a hard covering of the fruit.
The male flower of Casuarinaceae has a rudimentary perianth represented by an anterior and a posterior scale often one or both being absent and a single stamen; filament slender and anther bilobed; lobes dehiscing longitudinally.
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Female flower of Casuarinaceae is without a perianth; carpels 2 of which the posterior one is abortive with the result that ovary is unilocular; style short with 2 long filamentous stigmas; ovules 2, ascending orthotropous, only one maturing into a seed.
The mature carpel forms a winged nut; enclosed by the enlarged hardened bracteoles; seed without endosperm; cotyledons large. The nuts are aggregated into a dry cone-like structure and form a multiple fruit. The plants are monoecious; the male catkins are at the end of the branches and the female heads a little below. Flowers are wind-pollinated; the pollen grains are in tetrads and all develop pollen tube.
The leaves of Casuarinaceae , being very small and scale-like, the work of photosynthesis is carried on by the green branchlets; the pallisade cells are arranged in the ridges of these branchlets below the sclerenchymatous hypodermis; the stomata are sunken and situated in the furrows.
The branches of Casuarinaceae have two rows of vascular bundles, the outer or the cortical bundles are the leaf-traces; the inner bundles form a continuous ring with narrow medulary rays. The xylem-vessels usually have simple perforations.
The family of Casuarinaceae consists of only 1 genus, e.g., Casuarina with about 40 species occurring in Australia and S. E. Asia in dry or physically dry situations, therefore developing a xerophytic habit. Casuarina equisetifolia Forst. has been introduced into India and trees are often planted on road sides and parks.
They grow well on sea-shores and are much planted to check the advance of the sea. It is a quick-growing tree; the timber is hard but not suitable for planking. The wood yields good fuel. As regards the affinity of the family the discussion under the order may be seen.
