Casuarina equisetifolia, commonly known as coastal she-oak, horsetail she-oak,[3]ironwood,[4]beach sheoak, beach casuarina or whistling tree[5] is a species of flowering plant in the family
Casuarinaceae and is native to Australia, New Guinea, Southeast Asia and India. It is a small to medium-sized,
monoecious tree with scaly or furrowed bark on older specimens, drooping branchlets, the leaves reduced to scales in
whorls of 7 or 8, the fruit 10–24 mm (0.39–0.94 in) long containing winged seeds (
samaras) 6–8 mm (0.24–0.31 in) long.
Description
Casuarina equisetifolia is a monoecious tree that typically grows to a height of 6–12 m (20–39 ft), sometimes to 35 m (115 ft), and has bark that is smooth and greyish on young specimens, scaly or furrowed on older trees. The branchlets are drooping, up to 300 mm (12 in) long, the leaves reduced to scale-like teeth about 0.7 mm (0.028 in) long, arranged in whorls of 7 or 8 around the branchlets. The sections of branchlet between the leaf whorls (the "articles") are 5–13 mm (0.20–0.51 in) long and 0.5–1.0 mm (0.020–0.039 in) wide. Male flowers are arranged in spikes 7–40 mm (0.28–1.57 in) long in whorls of 7 to 11.5 per centimetre (per 0.39 in.) the
anthers 0.6–0.8 mm (0.024–0.031 in) long. The female cones are on a
peduncle 3–13 mm (0.12–0.51 in) long and sparsely covered with soft or woolly hairs. Mature cones are 10–24 mm (0.39–0.94 in) long and 9–13 mm (0.35–0.51 in) in diameter, the samaras 6–8 mm (0.24–0.31 in) long.[3][5][6]
Common names for the tree include Australian pine, horsetair tree, ironwood, beach sheoak; although it has features that seem superficially like a conifer, it is not a pine.[7]
Taxonomy
The genus Casuarina was first formally described in 1759 by
Carl Linnaeus in Amoenitates Academicae and the first species he described was Casuarina equisetifolia.[8][9] The specific epithet (equisetifolia) means "horsehair-leaved".[5]
Casuarina equisetifolia L. subsp. equisetifolia,[12] a tree 7–35 m (23–115 ft) high, the articles 5–8 mm (0.20–0.31 in) long and 0.5–0.7 mm (0.020–0.028 in) with 8 to 10 teeth 0.3–0.8 mm (0.012–0.031 in) long, the male spikes 7–40 mm (0.28–1.57 in) long, the cones 12–24 mm (0.47–0.94 in) long and 9–11 mm (0.35–0.43 in) wide on a peduncle 3–10 mm (0.12–0.39 in) long.[13]
Casuarina equisetifolia subsp. incana (Benth.) L.A.S.Johnson.[14] a tree 6–12 m (20–39 ft) high, the articles 7–13 mm (0.28–0.51 in) long and 0.7–1.0 mm (0.028–0.039 in) with 8 to 10 teeth about 0.7 mm (0.028 in) long, the male spikes 12–25 mm (0.47–0.98 in) long, the cones 10–20 mm (0.39–0.79 in) long, 10–13 mm (0.39–0.51 in) wide and densely covered with white to rust-coloured hairs, on a peduncle 3–13 mm (0.12–0.51 in) long.[3][15] The epithet incana means "white" or "hoary".[16]
There is some doubt as to whether Linnaeus' publication of C. equisetifolia is valid, since he based his description solely on
Rumphius's description of Casuarina litorea in
Herbarium Amboinense[17] and there are no
type specimens.[18]
Subspecies incana grows on rocky headlands near the coasts of eastern Queensland and New South Wales as far south as
Laurieton.[3][5][15][19]
Casuarina equisetifolia has been introduced to many other continents and islands.[2] It is an
invasive species in the United States, but biological control by insects, including by a Selitrichodes wasp and
Carposinidae and
Gelechiidae moths has been effective.[20][21][22] It is also regarded as being invasive in South Africa.[23]
Uses
Other than ornamental purposes, Casuarina was also explored in for its potential in remediation of textile dye wastewater. Casuarina leaves were found to be useful as absorbent material for the removal of textile dyes such as reactive orange 16[24] Rhodamine B,[25] methylene blue, malachite green[26] and methyl violet 2b.[27] Similarly the Casuarina dried cone was also reported to be able to remove Rhodamine B,[28] and methyl violet 2b.[29] The Casuarina bark was reported to able to remove methylene blue.[30] Even the Casuarina seed was also found to be useful in dye removal of neutral red and malachite green.[31] The carbon derived from the cones of Casuarina was found to be good absorbent for the landfill leachate,[32] while another laboratory also reported good absorbent for copper ions from aqueous solution.[33]
Culture
Names of places
In
Singapore, there is a road named
Tanjong Rhu Road because it once had many of these trees growing along the coast from
Kallang to
Rochor.[34] In the island of
Langkawi,
Kedah,
Malaysia, there is a sand spit in the mouth of the Ayer Hangat river in the
Kilim Karst Geoforest Park about 20 km from the town of
Kuah also named Tanjung Rhu where these trees line here.[35] The town of
Tanjung Aru in
Sabah is also named because a lot of this tree (aru) is found in its beach.[36]
Casuarina equisetifolia exhibits a high degree of adaptability to different environmental conditions, including coastal habitats, sandy soils, and disturbed areas. This versatility allows it to thrive in a wide range of ecosystems, increasing its potential for invasiveness.[38]
The species produces large quantities of winged seeds contained within cone-like structures. These seeds are easily dispersed by wind and water, facilitating the rapid spread of Casuarina equisetifolia over long distances. This dispersal mechanism enables it to colonize new areas and outcompete native species.[39]
Casuarina equisetifolia's lack of natural predators or pests contributes to its unchecked growth in many regions. While specific scientific references directly addressing this aspect might be limited, the absence of significant herbivory or predation on Casuarina equisetifolia in non-native environments has been observed in ecological studies documenting its invasive behavior [40][41]
Human activities such as urbanization, agriculture, and landscaping often contribute to the spread of Casuarina equisetifolia. The species is frequently planted for erosion control, windbreaks, and ornamental purposes, inadvertently introducing it to new areas where it can become invasive.[42]
^
abcdefBoland, Douglas J.; Brooker, M. I. H.; Chippendale, G. M.; McDonald, Maurice William (2006).
Forest trees of Australia. Collingwood, Victoria: CSIRO Publishing. p. 82.
ISBN0-643-06969-0.
^"Casuarina equisetifolia". Australian Biological Resources Study, Department of Agriculture, Water and the Environment: Canberra. Retrieved 29 April 2023.
^
ab"Casuarina equisetifolia subsp. incana". Australian Biological Resources Study, Department of Agriculture, Water and the Environment: Canberra. Retrieved 29 April 2023.
^William T. Stearn (1992). Botanical Latin. History, grammar, syntax, terminology and vocabulary (4th ed.). Portland, Oregon: Timber Press. p. 431.
^Rumphius, Georg E. (1743).
Herbarium Amboinense. Vol. 3. Amsterdam. p. 86. Retrieved 29 April 2023.
^Wilson, Karen L.; Johnson, Lawrence A.S. (1989).
Flora of Australia(PDF). Canberra: Australian Government Publishing Service. p. 201. Retrieved 29 April 2023.
^"Casuarina equisetifolia"(PDF). World Agroforestry (Centre for International Forestry Research). Retrieved 29 April 2023.
^Bharti, Vikash; Shahi, Amrita; Geed, Sachin; Kureel, M.K. (2017). "Biodegradation of reactive orange 16 dye in the packed bed bioreactor using seeds of Ashoka and Casuarina as packing media". Indian Journal of Biotechnology. 16: 216–221.