Monday, May 11, 2009

Lebronnecia kokioides

Lebronnecia kokioides

Lebronnecia kokioides, another monotypic genus (meaning this species is the only representative of the genus Lebronnecia), is an extremely rare small tree known only from the Marquesas Islands (Tahuata and Mohotani) in the South Pacific. It grows up to 10m high, with leaves up to 15cm long (usually less) that are somewhat pointed at the tip. Flowers grow 2-4 together on stalks up to 4cm long. The seed pod is a woody capsule that contains a single round black seed covered with reddish brown hairs.

When Lebronnecia was first described in 1966, only a single tree, along with a few seedlings was known from Tahuatu. By 1975, the forests on Tahuata had been seriously reduced due to grazing from goats, cattle, pigs and horses. Lebronnecia kokioides was later found on Mohotani, a neighboring island that is uninhabited by humans. Although the central portion of the island is forested, the northern portion, which was previously covered with xerophytic scrub, was reduced by sheep to a barren waste of red, stony soil. As early as 1910, the sheep were beginning to do severe damage to the remaining forests. Thankfully, Lebronnecia kokioides seems to be unpalatable to sheep. In 1971, a Nature Reserve was created on Mohotani, however the sheep still remain.

Lebronnecia kokioides is of considerable interest due to its geographical isolation and its relation to cotton (Gossypium). Included in the eight genera of the Gossypieae are four small genera with restricted geographic distributions (Fryxell, 1979): Lebronnecia, from the Marquesas Islands, Cephalohibiscus, from New Guinea and the Solomon Islands. Gossypioides, contains two species from East Africa and Madagascar and Kokia, endemic to the Hawaiian Islands, includes three extant and one extinct species.

Reference: Mohotani Island ―This is a small island about 20km cast of Tahuata. It is surrounded by sheer cliffs, which are up to 520m high on the straight, down-faulted east side. The surface slopes gradually in the form of a high plateau west and north from the main, high southeastern cliffs to the northern cliffs, which are about 460m above sea level.

In 1929 the greater pan of the island was forested, except for the plateau, which was covered by Miscanthus savanna with small areas of Thespesia (or more probably Lebronnecia or both). The forest on the rest of the island was composed of gigantic Pisonia, smaller Cordia suhcordara, Thespesia (or Lebronnecia), Pandanus, Aleurites, Hibiscus, and other trees and shrubs. Surface water was very scarce. Some time later, sheep were introduced. In 1968, when visited by Sachet, Oliver, and Schaefer, all undergrowth in the parts accessible to them except the malvaceous Lebronnecia, relative of Gossypium and poisonous with gossypol, had been destroyed by the sheep. Sheep avoided the Lebronnecia, giving this otherwise almost extinct shrub a new lease on life. Another Malvaceae, the arborescent, endemic Abutilon sachetianum, also persisted here. The condition of the tree layer of the forest was not reported.

   Vegetation of the tropical Pacific islands
   By Dieter Mueller-Dombois, Francis Raymond Fosberg
   Published by Springer, 1998