Fern  (Asplenium ascensionis)

Classified as Near Threatened (NT) in 2003 under IUCN Red List categories (3).

Asplenium ascensionis is a small, dark green fern found growing on rocky walls (2). The narrow, glossy fronds are composed of smaller leaflets known as ‘pinnules’. The pinnules are short and toothed at the edges (2).

This small fern is found on Ascension Island, South Atlantic; although some experts believe this fern is actually a variety of Asplenium erectum found on the island of St Helena (2). Previously much more common, Asplenium ascensionis formed part of a carpet of ferns that constituted the main vegetation of Green Mountain in the mid-19th century (2).

Found in damp, sheltered ravines on parts of Green Mountain at the centre of Ascension Island (2).

Ferns are ‘primitive’ plants that spread by releasing spores rather than by producing flowers and fruits. The distinctive frond stage of the fern lifecycle is asexual; spores are released from the fronds, which then germinate into minuscule heart-shaped structures known as ‘prothalli’. It is here that the sexual stage of the lifecycle occurs; male and female organs on the prothallus produce sperm and eggs respectively. If the female eggs are fertilised successfully, a new fern plant will begin to grow and the cycle starts again (4).

In Asplenium ascensionis however, the sexual stage of the lifecycle does not occur and the spore-producing plant develops directly from the prothallus (4).

The distribution of Asplenium ascensionis populations has declined and this species no longer represents part of the ground vegetation of the island. Loss of suitable habitat and competition with introduced species such as A. capillus-veneris is likely to have played a part in its decline; although these species may be able to exist together (3).

Recent evidence has revealed that Asplenium ascensionis is not under as much threat as previously feared. However, long-term monitoring of the population is still being carried out by Ascension Conservation (3).