It has reddish brown to grey bark; the bark is rough, brittle, peeling. Branchlets are pine-needle like, greyish green, jointed, thin (less than 1 millimetre wide), 10 to 20 centimetres (four to eight inches) long, minutely ridged, hairy in furrows. Leaves are reduced to tiny scales, six to eight in whorls (this is a distinguishing feature, see Similar Species), whorls encircle joints of branchlets. Flowers are unisexual/monoecious, inconspicuous, female in small axillary clusters, male in small terminal spikes. Fruit is a tiny, one-seeded, winged nutlet (samara), formed in woody cone-like clusters (fruiting heads), these clusters are brown, two-centimetre-long (3/4 inch) and 1.3 centimetre-wide (1/2 inch) (Description from FEPPC Undated).

This rapid-growing species will establish in habitats as varied as coastal sand dunes, high mountain slopes, the humid tropics and semiarid regions; it tends to be salt tolerant, wind resistant and adaptable to moderately poor solids; although it is not a legume it does have the ability to form root nodules with microbial associations and fix atmospheric nitrogen (NRC US Advisory Committee on Technology Innovation 1980; Little & Skomen 1989, in Snyder 1992).

The monthly mean maximum temperature in the native area of Casuarina is 10°C to 33°C and it is reported to prefer annual temperatures of 22°C to 27°C; it is not frost-hardy (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983; Snyder 1992). This lowland species grows from sea level up to 1 500 meters; in its natural habitat rainfall is from 700 to 2 000 millimetres, often with a dry season of six to eight months; however, it is reported to tolerate an annual precipitation of 640 to 4 300 millimetres (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983).

This species tolerates calcareous (limestone-derived) and slightly saline soils with a pH of between 5.0 and 7.7 but it grows poorly on heavy soils such as clays; it can withstand partial water-logging for a time (NRC US Advisory Committee on Technology Innovation 1980; Duke 1983). It is reported to prefer coarse-textured soils (Rockwood et al undated) and is very tolerant of saline conditions and salt spray (Elfers 1988).

Habitat alteration: The thick layer of leaves produced by C. equisetifolia has a reduced food value for native wildlife and destroys habitat for native insects and other wildlife (Klukas 1969, in Snyder 1992).

Reduction in native biodiversity: C. equisetifolia forests provide little or no native wildlife habitat. In the Everglades, where C. equisetifolia has invaded south Florida’s hammock and tree island communities, Mazzotti Ostrenko and Smith (1981) studied the effects of Melaleuca quinquenervia and C. equisetifolia on three native rodents (Peromyscus gossypinus, Sigmodon hispidus and Oryzomys palustris). The authors found that Casuarina habitats supported fewer rodents than either cocoplum or Melaleuca habitats.

Threat to endangered species: C. equisetifolia displaces native beach vegetation that provide critical wildlife habitat for threatened and endangered plant and animal species. C. equisetifolia forms dense stands and destroys reptile breeding sites in the Everglades National Park. Its presence threatens the only remaining nesting areas in the USA of the ‘Vulnerable (VU) American crocodile (Crocodylus acutus) and one of the remaining most productive nesting areas of the ‘Endangered (EN)’ loggerhead turtle (Caretta caretta ssp. caretta)) and the ‘Endangered (EN)’ green turtle (Chelonia mydas) (Binggeli 1997; Klukas 1969 1973, in USDA Forest Service 2007). The nest sites of these species are threatened as the invasive plant takes over beach dune habitat and baby sea turtles become trapped in its roots as they emerge from their nests (Florida DEP Undated). Areas inhabited by the ‘Vulnerable (VU) gopher tortoise (Gopherus polyphemus) are also threatened with invasion by Casuarina (Mazzotti Ostrenko and Smith 1981).

Modification of hydrology: C. equisetifolia can exhaust the moisture in the soil and lower the water table of the area (NRC US Advisory Committee on Technology Innovation 1980) it invades.

Physical disturbance: C. equisetifolia can facilitate beach erosion by displacing deep-rooted vegetation (Florida DEP Undated). Unlike native vegetation C. equisetifolia has a shallow root system and tends to uproot and topple during high winds, posing a significant hazard to coastal storm evacuation routes (Florida DEP Undated). Its dense roots can also break water-lines and sewer-lines (Snyder 1992).

Inhibits the growth of other species: C. equisetifolia produces allelopathic compounds that inhibit growth of other plants (Morton 1980, in Florida DEP Undated).

Modification of successional patterns: C. equisetifolia can be a primary or secondary coloniser in disturbed areas in Florida, USA (Elfers 1988, Klukas 1969, in Snyder 1992).
Human health: The genus Casuarina poses a problem to humans as its pollen is a source of respiratory irritation and allergies (Elfers 1988; Binggeli 1997).

Physical: For small infestations the manual removal of seedlings and saplings is recommended (Swearingen 1997); however, it should be noted that cutting often induces sprouting (Snyder 1992).
Prescribed fire has been used for large infestations in fire-tolerant vegetation communities. Fire control is reported to be effective in dense stands with sufficient dry fuel on the ground. Periodic fires coupled with the use of herbicides may be an effective method of controlling Casuarina (Snyder 1992). However, too frequent intense fires that kill over story native pines may actually encourage Casuarina species to establish (Wade Ewel & Hofstetter 1980, in Snyder 1992). Burning Casuarina in peat soils may be hazardous (Morton 1980, in Snyder 1992). Fire may be an effective control method for trees greater than eight centimetres (three inches) in diameter and in dense stands; burning could be potentially harmful if the soil pH is changed such that native species cannot establish (Elfers 1988, in Snyder 1992).

Chemical: For heavier infestations application of a systemic herbicide to bark, cut stumps or foliage is likely to be most effective. Chemicals such as 2,4,5-T, 2,4-D or Garlon 3A can be used to tackle Casuarina (Klukas 1969, Morton 1980, in Snyder 1992). A 2% mixture of Garlon 4 in diesel oil applied using the basal bark method or the hack-and-squirt method is most commonly used against Casuarina in the USA (US Exotic Pest Plant Council Undated). Garlon 3A is also effective.

Biological: USDA Agricultural Research Service (ARS) scientists have been searching in Australia's outback and coastlines for insects that could be key bio-controls for C. equisetifolia (Flores 2008). From 300 species, including wasps, weevils, stem-borers, sap-suckers and seed-eaters about 12 candidates have been identified. Not only do these agents attack C. equisetifolia but many also attack the related invasives C. glauca and C. cunninghamiana. The most promising bio-control agents include the seed-feeding wasp (Bootanelleus orientalis), which is host-specific to Australian pine, and the defoliator moth (Zauclophora pelodes). These insects are still undergoing testing to determine their suitability for use as bio-control agents in the United States. Please follow this link to read more about this research in the September 2008 issue of Agricultural Research magazine.
Many pathogens threaten plantations of Casuarina in many parts of the world. In India a stem borer kills shoots and seedling damping-off by Rhizoctonia spp. occurs in nurseries (Binggeli 1997). Nursery seedlings in India are attacked by various insect species. In China the lymantriid moth (Lymantria xylina) is described as one of the worst pests of C. equisetifolia (Elfers 1988).
In Florida, USA, there has been a high rate of root rot caused by the fungus Clitocybe tabescens. In Puerto Rico stem canker and dieback attributable to the fungus Diplodia natalensis have been recorded on C. equisetifolia. In Puerto Rico natural regeneration is rare because ants eat nearly all the seeds (Binggeli 1997). Ants have also reportedly been a major source of control in India.

Integrated Pest Management: Recently disturbed beach habitat may be planted with native vegetation to prevent C. equisetifolia from invading.