Pisonia  (Pisonia sechellarum)

Classified as Endangered (EN) on the IUCN Red List (1).

Found in just one valley on an island in the Indian Ocean (1), Pisonia sechellarum is a tall tree with smooth, spongy bark that is capable of retaining water (2). The green leaves, measuring up to 30 centimetres long, grow in a spiral arrangement around the stems (3). Small, pale yellow flowers, just half a centimetre long (3), grow in clusters of three to four (2). The fruits of this plant are fleshy, sticky and olive green in colour, growing up to four centimetres long (2) (3).

Endemic to the Seychelles, Pisonia sechellarum currently occurs only in a single valley on the island of Silhouette (1), although historically it may have also occurred on the island of Mahé (3).

The tiny remaining population of Pisonia sechellarum grows in a valley at 400 to 550 metres above sea level (2).

Like other species of Pisonia, the sticky fruits of Pisonia sechellarum adhere to the fur or feathers of animals (2), resulting in the dispersion of the seeds contained within the fruit. The leaves of this plant are a popular food of insects, particularly moths of the Epicroesa genus, and it is unusual to find a tree that does not bear the marks of an insect feeding bout (2). Epicroesa moth species are also said to feed on the tree’s seeds, but repay this predation by carrying out the vital task of pollination for the tree (1).

In the past, large areas of forest on Silhouette were cleared, with only forest in the steep and inaccessible areas of the island left untouched (2). As a result, an area covering just half a hectare harbours the remaining Pisonia sechellarum (1), a population which was estimated to contain just 190 trees in 1990 (2). This small population suffers from suspected low genetic diversity and a poor rate of seed germination (1), factors which my hinder the population’s recovery and threaten its survival.

The small area in which Pisonia sechellarum occurs lies within forest protected by the Nature Protection Trust of Seychelles (NPTS) (1). The NPTS established the Silhouette Conservation Project in 1997 and has since been protecting the island’s environments and endeavouring to restore them to a near-natural state (4). Through the valuable work of the NPTS, which includes conducting research into the animals and plants of the island and efforts to control invasive species (4), hopefully the exceptional biodiversity of this island, including Pisonia sechellarum, will be preserved.

For further information on conservation in the Seychelles see:

• Nature Protection Trust of Seychelles:
  http://islandbiodiversity.com
• Nature Seychelles:
  www.natureseychelles.org