Trigonobalanus and the Tropical Amphi-Pacific Element in the North Andean Forest

Abstract

The tropical montane Andean forest flora contains almost 10% of woody genera with an American-Asiatic distribution (i.e. a 'tropical amphipacific' one). Trigonobalanus is one of the most striking examples of this distribution. As many of the genera of this phytogeographical element occurred in the subtropical to temperate holarctic Tertiary flora which gradually migrated southward during the gradual cooling of the climate in the Late Cenozoic, the simplest and most probable theory to explain their presence in the Andes is that they migrated into South America as soon as the formation of the Panamanian land connection permitted this, just like the recent holarctic elements did. The theory suggests a geologically late arrival for all these genera, those adapted to a warmer climate being able to cross first, those adapted to a cooler climate relatively later. The available palaeobotanical and palynological data confirm this suggestion, which gives the theory a high degree of probability.