Guayana Highlands BioProvince
This BioProvince (as defined by Armen Takhtajan) comprises the Guayanan Highlands situated east of the Andes. The area covers much of southern Venezuela and in addition to Guayana it extends marginally into Brazil and Colombia. Of considerable interest are the many spectacular tableaux (tepuis), which were the inspiration behind the legendary 'Lost World' of Sir Arthur Conan Doyle (1912). The indigenous name for these plateaux is tepuis and the biogeographical area comprising all of the tepui is called Pantepui. Many are graced with spectacular waterfalls including Angel Falls - the highest waterfall in the world at 979 m. The highest tepui is Pico da Nebline at 3,014 m. Others include Pico Phelps (2992 m), Roraima-tepui (2810 m) and Cerro Marahuaka (2800 m). They are relicts of a former, ancient sandstone peneplain created between 1.6 and 1 billion years ago, and it is thought that the sand came from the easterly uplands of the ancient Gondwana continent where it was deposited in a shallow sea or large inland lake. Below the sandstone the basement rock comprises the Guayana Shield, which consists of a variety of igneous and metamorphic rock types that formed during the Archean and Proterozoic times some 1.8 billion years ago and represents one of the oldest geological formations in South America. The tropical climate includes abundant rainfall with little or no dry season in the higher upland areas. As a result the valleys contain deep, boggy acidic soils that have become peaty to a depth of several metres. The flora, which is thought to be extremely ancient, is very distinctive with one endemic family (Hymenophyllopsidaceae), about 168 endemic genera, and of the 8000 species recorded for the area, about 4000 are endemic. There is also a recently recorded endemic subfamily, the Pakaraimoideae of the Dipterocarpaceae. It includes the tree Pakaraimaea dipterocarpacea and prior to its discovery dipterocarps were thought to be confined the palaeotropics. This and distribution of the family Rapateaceae provide support for an ancient connection between the Guayana Shield flora and other floras such as those of Malaysia and Gondwanaland. Studies show that speciation has occurred at different altitudinal levels, not only on the tepui summits, but also on the talus slopes and bluffs and even at the base of tepuis. The family Bromeliaceae, for example, has been especially successful in the evolution of new cliff dwelling species.
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|