One is often blown away by the strangeness and innocence of the animals surrounding us on our walks through the Enchanted Islands, that the unusual vegetation either escapes our notice, or is not given its due importance. In many ways, however, the flora is as spectacularly weird as the fauna! The plants of the Galapagos Islands exerted a great influence on Charles Darwin during his visit here in 1835, as his interest in plant geography and dispersal mechanisms was closely tied to the collections he made at this time. These specimens were the basis of the first scientific guide to the flora of the archipelago, composed by Joseph Hooker, a great supporter and friend of Darwin's.

It first comes as a shock to find such arid, desert-like vegetation on islands found right on the equator, where one would expect lush tropical vegetation. However, the cold waters that bathe the coastal areas of the archipelago create desert-like conditions, where the only plants able to survive are those adapted to extreme dry conditions, such as drought-deciduous trees and succulents. The most extreme examples of the latter adaptation are the cacti, and we have spectacular examples of these in Galapagos. Two of the cacti genera are endemic to the islands, the candelabra genus, Jasminocereus, including three species, and the little lava cactus,Brachycereus nesioticus, a pioneer cactus of which one species is present. The third genus of cacti found here is one that is well known throughout the arid parts of the American continent, the Opuntia or prickly pear. The Galapagos Opuntias however are a very interesting group, both because they have diverged to form a total of fourteen types and because some of these have evolved into tall trees. These species thought to have evolved from two ancestral stocks, and are found as two main morphological types. On islands devoid of terrestrial tortoises and iguanas, low shrubby forms of Opuntia are found, similar to the ancestral cacti. On islands that have tortoise populations though, one gets tall tree-like forms that have a reddish, flaky bark and heavy spines. The relationship between the giant tree Opuntias and giant tortoise distribution suggests that the main reason the cacti evolved this way was to avoid browsing by these massive herbivores; these in turn evolved into what is known as the saddle-backed variety in areas where the main food source are these cactus trees. Saddle-backed tortoises have taller fronts to their carapace, long legs and long necks, in order to reach up to the succulent pads. This is a perfect illustration of what is known as a "biological arms race".

On our walk into the research station, we routinely observe some of the tallest cactus trees in the Galapagos, as they can reach up to 12 meters (Up to 37ft) high, with a trunk width over three feet, well outsizing our tallest naturalist, Daniel!