Argusia  (Argusia argentea)

Arugsia argentea is classified as Least Concern (LC) on the IUCN Red List (1).

Argusia argentea is a medium-sized shrub that grows along tropical coastlines. It typically reaches heights of around six metres, with the canopy spreading to around nine metres in diameter. A particularly conspicuous feature of this species is its light green, silky, haired leaves, which have a silvery-grey sheen (2) (3). The leaves are rather fleshy, oval in shape and are arranged alternately, but spiral at the branch tips (4). The small, white flowers are arranged into attractive inflorescences, with five-lobed sepals and petals. The bark is light brown or grey, with deep grooves. The smooth, elongated fruit is greenish-white to brown, and divides into four pale ‘nutlets’ which turn light brown when dry. The fruit encases two to four seeds. In adaptation to its sandy, coastal environment, Argusia argentea has very strong roots that anchor the plant in even the loosest sand and most severe winds (2).

Argusia argentea is native to Madagascar and tropical Asia in the Indian Ocean region, as well as Australia and many tropical islands in the Pacific. It has been introduced to the Hawaiian Islands (2) (4).

Argusia argentea is most commonly found on sandy shores with lots of coral debris, on tropical islands and coral cays. It is an early coloniser of these hot, salty, windswept environments, but over time tends to be shaded out and replaced by larger, slower-growing trees. On the Australian mainland, Argusia argentea also grows in beach forest (3).

Argusia argentea reaches maturity after several years of growth, when it typically begins to flower throughout the year. The flowers attract large numbers of butterflies and bees, which are the main pollinators. Argusia argentea also produces fruits year-round. Germination takes two to four weeks, with the seeds maturing when the fruit turns translucent and becomes soft. The seeds are enclosed in a corky tissue that turns from white to brown with exposure to air. Argusia argentea is a slow growing species, with a lifespan of at least several decades (2).

Although still widespread and relatively abundant in most areas, in some places Argusia argentea is rare and threatened. Growing on shorelines, Argusia argentea is a handy firewood, often leading to over-collection. On many islands, Argusia argentea is very important in traditional cultures and rituals. Its leaves are often eaten and used as a traditional medicine to treat rashes, diarrhoea and bruising, and to stop bleeding. The wood may be used to make craft items, tools and canoes, and used in construction. Such exploitation of this species can lead to local population declines (2). 

On Pitcairn Island in the southern Pacific Ocean, Argusia argentea is threatened by habitat loss and competition with introduced species for natural resources (5). These threats began soon after the arrival of early settlers on the island, with lowland forests cleared for construction, agriculture and firewood. Exotic species were introduced to the island, sometimes deliberately, and cultivated plants established in the wild (6). One such species, the fruit tree Syzygium jambos¸ was initially introduced to provide firewood, but now that it is rarely used for this purpose, the species is spreading rapidly across the island and threatening much of the native flora (6). Today around half of the Pitcairn flora is threatened with extinction, with less than 30 percent of the island covered in natural vegetation (7).

In the absence of any major threats to its survival, Argusia argentea has not been the target of any known conservation measures. In many areas it is cultivated in commercial nurseries for use in coastal stabilisation, landscaping and planting on streets and in parks (2). 

On Pitcairn Island, the most urgent conservation requirements for the island’s flora are the clearance of invasive species, tackling habitat loss and the establishment of ex-situ conservation measures for some of the most threatened species (5) (7). Efforts are already underway to remove exotic species, and Syzygium jambos is being controlled by making cuts into the tree’s trunk and injecting poisonous chemicals to kill it. It is also thought that much of the island’s threatened plants could be protected by the establishment of a system of reserves, and the replanting of native plants after the clearance of exotic species (7) (8).

ARKive is supported by OTEP, a joint programme of funding from the UK FCO and DFID which provides support to address priority environmental issues in the Overseas Territories, and Defra

Find out more about conservation on Pitcairn Island:

• Procter, D. and Fleming, L.V. (1999) Biodiversity: the UK Overseas Territories. Joint Nature Conservation Committee, Peterborough, UK.
• National Botanic Gardens, Glasnevin:
  http://www.botanicgardens.ie/herb/pitcairn.htm