This BioProvince (as defined by Armen Takhtajan) comprises the Galapagos archipelago - a group of 121 Pacific islands all of volcanic origin. However, only about 13 are large enough to support extensive vegetation, and of these, Isabela is the largest with an area of 4588 ha and reaching a height of 1700 m. These volcanic islands like Hawaii and other oceanic islands are thought to be the product of a mantle plume, with each island being created over a magma hot spot and then moved away by plate tectonics. Cold-water currents (Humboldt Current) moderate the tropical climate but generally speaking the days are warm and the nights are cool, and humidity is usually low. The vascular plant flora consists of about 863 species, sub-species and varieties although only about 543 are considered to be indigenous, and of these up to 231 species and sub-species are considered to be endemic. Seven endemic genera are recognised including Darwiniothamnus, Lecocarpus, Macraea, Scalesia (Asteraceae), Brachycereus, Jasminocereus (Cactaceae) and Sicyocaulis (Cucurbitaceae). The majority of the native flora and endemics are of western South American origin but there are also small Central American, Northern American, Mexican and West Indian elements. The level of endemism is surprisingly low compared to say Hawaii but this is attributed to their dry climate and relative nearness to the mainland. Nevertheless, there are some excellent examples of adaptive radiation. From what is believed to have been single ancestral forms, Scalesia has given rise to 20 taxa, Mollugo 9 taxa, Alternanthera 8 taxa, and there are an additional 15 genera that have given rise to more than 3 taxa.
The natural plant formations can be divided into six or seven altitudinal zones. Starting at sea level these include the littoral or coastal zone, the arid zone (immediately inland of the littoral zone between 80 and 300 m), the transitions zone (above the arid zone to an elevation of about 320 m), the Scalesia zone (on larger islands from 180 to 550 m), the Zanthoxylum zone (a transitional zone that can sometimes be recoginised), the Miconia zone (between 400 and 700 m) and the fern-sedge zone (from 500 m to the summits of many of the volcanoes). As far as endemics are concerned, most (about 137) are found in the arid zone, which is probably partly due to the fact that this is the most extensive zone, followed by about 56 in the Scalesia zone. The transition zone has about 17, the littoral zone about 10, the fern-sedge zone about 9, while the Zanthoxylum and Miconia zones probably only have about one each.
The following accounts for this BioProvince have been written or will be written with particular reference to endemic and locally important species. Accounts available are displayed in green or yellow. Those displayed in red are either in the pipeline or awaiting expert contributions.
|Endemic Vascular Plant Flora|