Family: Casuarinaceae
Common name: Casuarina, Horsetail casuarina, Coastal she-oak, Common Rhu, Mile tree, Horsetail she-oak, Horsetail tree, Ironwood, Southsea ironwood, Beach sheoak, Beach casuarina, Whistling tree, Australian pine
Casuarina is a fast-growing evergreen tree that is well known for its strikingly unique leaves, and resilience in harsh environment conditions.
It is native to the tropical and subtropical regions of Southeast Asia like India, Bangladesh, the Andaman islands, Vietnam, Thailand etc., and it has been successfully introduced to a number of other countries along the same latitude. They grow very well along beaches and coastlines, since they are tolerant of salinity and strong winds.
Tree characteristics
Casuarina trees are can grow to a height of 25-35 meters very quickly, with a tall, straight bark that is smooth when the tree is small, but grows rough, scaly, fissured as the tree matures. The structure of the trunk and arrangement of leaves contribute to its resemblance to pine trees.
Roots of Casuarina trees are fibrous and well-developed, helping them adapt to beaches with strong winds. The roots also contain nitrogen-fixing bacteria like the plants in the Fabaceae family, which makes these trees beneficial for improving the soil health.
The long, needle-like structures that hang from the stem are not actually leaves, but modified branches. True leaves are reduced to small, scale-like structures, about .5-1 mm long, that are seen on the green branches – they are very inconspicuous. So these modified branches that contain chlorophyll perform photosynthesis instead of the leaves.
The long, drooping branches of the Casuarina tree look like horse tails, giving the tree its name Horsetail Casuarina. These branchlets are 20-30 cm long, arranged in large whorls. Each individual green twig is made of small segments which can be separated easily by just pulling them apart.
Casuarina trees can be monoecious or dioecious, which means that the male and female flowers can be produced on the same tree or on different trees. Both male and female flowers are produced in small bunches, both very small in size, the male flowers slightly larger than the female flowers.
Male flowers are produced as long, cylindrical, yellow bunches that release huge amounts of pollen. Female flowers appear as small, spherical clusters at the ends of branches.
After pollination, the female flowers produce small, woody cones that contain numerous seeds. They are 2-4 cm long and resemble those of pine trees, though the tree is not an actual pine.
Casuarina fruits are initially green, ripening to a brown color on maturity. The seeds are small, dark, and winged, helping in wind dispersal.
Gardening tips
Casuarina trees are excellent wind breakers in coastal areas, where they are grown in clusters or rows to prevent wind damage to structures. They can be grown in home gardens, since they are very resilient and easy to take care of.
These trees need full sunlight for optimal growth and flowering. Their root system can be very aggressive, and hence it is very important that they are not planted near the house or any structure where the foundation is very close to the tree.
Casuarina trees can grow in a variety of soil conditions, and are tolerant of drought, wind, extreme weather conditions, and most pests. Watering is needed only when the tree is small, after which it can pretty much take care of itself. They can be pruned into desired shapes if you do not wish the tree to be very tall.
Uses of Casuarina tree
Casuarina trees are mostly grown as wind breakers along beaches, or as ornamental trees. Parts of the tree have some medicinal uses in the treatment of stomach ailments, ulcers, wounds, skin infections, diarrhea, and inflammations.
The capability of the Casuarina roots to fix atmospheric nitrogen make them very valuable in improving poor soil. The leaves and bark of the tree have the capability to remove industries dyes and other impurities from water.
The wood is strong and durable, used for making furniture, posts, and implements. It is also burnt as firewood and is preferred for its high heat output.
Casuarina trees are considered invasive in some countries due to their fast-growing nature and capability to germinate quickly from seeds.
Propagation
Propagation is through seeds and stem cuttings.
Seed propagation is a very effective method since seeds can be collected easily from mature fruits. Collect fresh, dry seeds from the tree and plant them in moist soil to germinate. Stem cuttings taken from young semi-hard branches can also take root in soil very quickly.
Photographed at: Chethy beach, Alleppey, Kerala
