Darwin and the Plants of the Galápagos-Islands

Abstract

During his five year sea voyage with the “Beagle”, Darwin, at the suggestion of the botanist J.S. Henslow, collected more than 1400 vascular plants, and more than 200 of them alone during his short stay on the Galápagos Islands. The unique collection of plants from the Galápagos archipelago was examined in 1845 by J.D. Hooker. Unlike the birds, Darwin had collected the plants separately for each island. Hooker described 78 of them as new species and analyzed the close biogeographical relations of the Galápagos flora with the South-American continent. The finding that more than 50% of the species are not found anywhere else on the globe – are hence endemics, many of them restricted to individual islands – was a sensation for Hooker and Darwin. Hooker correctly characterized the Asteraceae as the most remarkable family of the Galápagos Islands, due to the great number of their endemic genera and species. He also discussed the adaptations which might have allowed the plants of the different families to reach the isolated islands. Hooker’s results played an important role for Darwin in his developing the theory of evolution, and – besides the examples of birds, tortoises, and lizards – provided him with weighty arguments to defend it. There are seven endemic plant genera on the Galápagos Islands, and 19 genera that are adaptively diversified. With 19 endemic taxa, the genus Scalesia (Asteraceae) is the most spectacular example of an adaptive radiation, followed by the prickly pear cactuses (Opuntia) with 14 endemic taxa. While Darwin’s finches meanwhile represent one of the best-studied examples of evolution and adaptive radiation, only little research has been done so far into evolutionary processes in plants of the Galápagos archipelago. The prominent role that Darwin’s plants played for his scientific insights is even less known.