Coastal she-oak
Casuarina equisetifolia L.
Casuarina equisetifolia (coastal she-oak, horsetail tree) is a coastal tree of the family Casuarinaceae. Its green, jointed, whorled branchlets — resembling a horse’s tail — carry out photosynthesis (the true leaves are reduced to scales), allowing it to withstand salt-laden winds, hot sand and poor soils, with the help of nitrogen fixation by the symbiotic actinomycete Frankia. The very hard, heavy, termite-resistant wood is used for poles, firewood and charcoal, and the bark is rich in tannins. Casuarina is planted as coastal windbreak and sand-binding belts along Vietnam’s coast. IUCN lists it as Least Concern (LC).
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Coastal she-oak — Fruit & seedsCoastal she-oak — Whole treeCoastal she-oak — Fruit & seedsOverview
Casuarina equisetifolia (coastal she-oak) is an evergreen tree 6–35 m tall (usually 10–20 m) with a straight trunk and grey-brown, lengthwise-fissured bark. The true leaves are reduced to tiny scales borne in whorls of 6–8 at the nodes of green branchlets; it is these green, jointed, whorled branchlets — resembling a horse’s tail — that carry out photosynthesis. The tree is monoecious or dioecious: male flowers in small spikes at the branchlet tips, female in axillary clusters. The fruit is a small woody, cone-like cluster holding winged seeds; the tree grows fast.
Updated by lebachungtdh@gmail.com · 10/09/2026
Casuarina equisetifolia is native to the coastal areas of northern and eastern Australia, South-East Asia and the Pacific islands, and is now planted throughout the tropics and subtropics. It withstands salt-laden winds, hot sand, drought and nutrient-poor soils thanks to root nodules formed with the symbiotic actinomycete Frankia, which fixes atmospheric nitrogen. This makes it a key species for coastal windbreak and sand-binding forests along Vietnam’s coast from north to south; however, its nitrogen fixation can also alter soils and make it invasive in some areas outside its native range.
Updated by lebachungtdh@gmail.com · 10/09/2026
Casuarina wood is very hard and heavy (high density), red-brown in colour, resistant to termites and decay, and regarded as an ironwood; it consists mainly of cellulose with a high lignin content (explaining its hardness and durability), hemicellulose and extractives. The bark is rich in tannins and therefore astringent, used for tanning and dyeing; other parts contain flavonoids and polyphenols. Because the wood is heavy and gives off much heat, casuarina is a good source of firewood and charcoal.
Updated by lebachungtdh@gmail.com · 10/09/2026
Casuarina is widely planted as windbreaks, sand binders and against coastal erosion — an important role in many Vietnamese coastal provinces. The wood is used for poles, posts, farm tools, load-bearing items and stakes; wood and small branches make firewood and high-quality charcoal. The bark yields tanning tannins and dye; the tree is also used for shade, ornament and hedging. In folk medicine the astringent bark is used for diarrhoea, and the tree is planted to green sandy soils and improve land.
Updated by lebachungtdh@gmail.com · 10/09/2026
Casuarina equisetifolia is listed as Least Concern (LC) by IUCN and is widely planted throughout the coastal tropics; in some areas outside its native range (such as Florida and parts of Africa) it becomes an invasive species requiring management because its nitrogen fixation alters soils. As for safety, its parts are not a common food; the wood and dust can irritate the respiratory tract during processing, and the pollen can cause allergy. Using the bark as medicine should follow verified experience and professional guidance.
Updated by lebachungtdh@gmail.com · 10/09/2026
Life cycle
From seed to productSeed
Tiny winged seeds disperse by wind and water; sown in moist sand, they germinate quickly after rain.
Sapling
Seedlings root deeply, tolerate hot sand and salt wind, and grow fast to form green belts.
Mature tree
Trees 6–35 m with a fine, evergreen canopy provide effective shade and wind protection.
Fruiting
Small woody, cone-like capsule clusters ripen and open to release winged seeds.
Distribution & origin
Share of recorded occurrences by region- Australia (native)22%
- Vietnam (coastal)24%
- South-East Asia (Indonesia, Philippines, Thailand…)18%
- Pacific (Melanesia, Polynesia)10%
- South Asia (India, Bangladesh)8%
- Africa and the Middle East (planted)8%
- Americas and elsewhere (planted)10%
Chemical composition
Relative content in agarwood resin- Cellulose (wood)Main wood component40%
- LigninLignification; gives hardness and weight24%
- HemicelluloseWood polysaccharide14%
- Tannins (bark)Astringent; tanning and dyeing10%
- Flavonoids and polyphenolsAntioxidant6%
- Others (extractives, minerals, oils)Minor components6%
Uses
- Coastal windbreaks, sand binding and erosion control
- Wood for poles, posts, farm tools; termite-resistant
- Firewood and high-quality charcoal
- Bark for tanning tannins and dye
- Shade, ornamental and coastal hedging
- Folk medicine (astringent bark) and greening sandy soils
Properties
- Branchlets
- Green, jointed, leaf-like
- Wood
- Reddish-brown, very hard, heavy
- Salt tolerance
- High, suited to coastal sand
Habitat & conservation
Coastal beaches, sand dunes and well-drained sandy soils; tolerant of salt wind, drought and nitrogen-poor soils thanks to nitrogen-fixing symbiosis with the actinomycete Frankia. It often forms coastal and estuarine forests in tropical and subtropical regions.
Conservation
Not globally threatened (IUCN: LC); widely planted throughout the coastal tropics. In some areas outside its native range (such as Florida and parts of Africa) it becomes an invasive species requiring management because its nitrogen fixation alters soils.
References
- 1Plants of the World Online — Casuarina equisetifolia L. — Kew Science, 2024
- 2IUCN Red List — Casuarina equisetifolia — IUCN, 2019
- 3CABI Invasive Species Compendium — Casuarina equisetifolia — CABI, 2022
- 4Casuarina equisetifolia — coastal she-oak, description and uses — English Wikipedia, 2026
- 5Phi lao — đặc điểm, vai trò chắn gió, công dụng — Vietnamese Wikipedia, 2026
- 6Nguồn ảnh: Sam Fraser-Smith (CC BY 2.0) — Wikimedia Commons,
- 7Nguồn ảnh: lienyuan lee (CC BY 3.0) — Wikimedia Commons,
- 8Nguồn ảnh: Eric Guinther (CC BY-SA 3.0) — Wikimedia Commons,
- 9Nguồn ảnh: Bruce Bailey (CC BY 4.0) — Wikimedia Commons,
- 10Nguồn ảnh: Forest and Kim Starr (CC BY 3.0 us) — Wikimedia Commons,