In the north this BioProvince (as proposed by Peter Martin Rhind) includes the dry forests along the Caribbean coast as far as the Sierra Nevada de Santa Marta, and south into the Cauca and Magdalena valleys. Moving south it extends from the Panama Canal, south and east into the wet and moist forests of Panama's Darién province, and then through the Chocó region of western Colombia and the moist forests along the west coast of Ecuador and into the dry forests of southern Ecuador and extreme northwestern Peru. This latter area is often called the Tumbesian Centre (after Tumbes department of Peru) but it is primarily centred on El Oro and Azuay provinces in southwest Ecuador and Tumbes and Piura departments in northwest Peru. The Darien province is the extensive flat valley in Panama bisected by the Chucunaque and tributary rivers. The Caribbean coastal mountains form its eastern border and the low Pacific coastal range form its western border. Panama represents part of the isthmus that formed between North and South America some 3 million years ago in the late Pliocene epoch and is thought to be one of the most important geologic events to happen on Earth in the last 60 million years. Apart from shutting down the flow of water between the Pacific and Atlantic oceans and causing major oceanic circulation changes including the development of the Gulf Stream, it played a major role in altering the World’s biodiversity by allowing the migration of plants and animals between two previously isolated continents. As a result of this intermixing Panama has a higher biodiversity than almost anywhere else on Planet.
The area as a whole is mainly made up of alluvial plains of recent origin and low mountains formed from sediments of Tertiary and Pleistocene ages. In the Chocó zone (mostly in Colombia) the climate is aseasonal with some of the highest recorded rainfall on the Planet, which can be up to 9000 mm/year, but in one locality 11,770 mm/year were recorded. Consequently it also has some of wettest rain forests on the Planet, and these possibly represent the only true pluvial forest in South America. This has created extreme levels of biodiversity particularly for plants, amphibians, butterflies and birds. In fact, it is considered one of the most species rich lowland areas in the World. The rainfall, however, is less pronounced in more northern areas toward Panama and the Caribbean Sea and also in more southern areas. The flora is extremely rich with an estimated 9000 vascular plant of which some 2750 are endemic. There are no endemic families, but a number of the endemic genera such as Cremosperma (Gesneriaceae) and Trianaeopiper (Piperaceae) have undergone considerable amounts of speciation. One of the botanical peculiarities of the white clay flora in the Chocó region of Bajo Calima, Colombia is the large number sclerophyllous leafed species with unusually large leaves and fruit. One species, Psittacanthus gigas (Loranthaceae) possibly has the largest simple leaves in world measuring 1 m long and 50 cm wide. Other species, such as Iryanthera megistophylla (Myristicaceae), Licania gentryi (Chrysobalanceae) and Schlegelia dressleri (Bignoniaceae) have the largest leaves in the World in their respective families and many others appear to have the largest leaves of their respective genera. Large fruit size appears to be a reflection of the fact that many plants have their fruit and seeds dispersed by mammals, whereas wind dispersal is uncommon. Sacoglottis ovicarpa has the largest fruit of its family (Humiriaceae) and Orbignya cuatrecasana is only exceeded in fruit size in the palms by the coconut taxa Cocos and Lodoicea, and several endemic species of the Myristicaceae have the largest fruit in their genera (e.g. Compsoneura and Iryanthera).
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.
|Vascular Plant Flora|