Galapagos is typical of oceanic islands in having a very small native flora - only some 500 vascular plant species, of which 180 are endemic. These arrived or evolved over the 3 million years or so of the existence of the present Galapagos islands, at a rate of about one species arriving every 10,000 years.
In striking contrast, more than 640 vascular plant species have been introduced by people to Galapagos, about 90% of them deliberately, since the discovery of Galapagos by humans, i.e. at a rate of about 1.3 species per year. The 90% are useful plants, including fruit, vegetables and other crops, timber trees, medicinal plants and ornamentals.
The relatively few accidentally introduced plants are mostly pan-tropical or European weeds of disturbed areas, which have often spread widely in Galapagos because of the open, “naturally disturbed” character of much of the environment in the archipelago. However, the accidentals have rarely been the cause of major problems for the native biota, whereas many of the plants introduced for cultivation have escaped and are now threatening native species and habitats.
The worst are habitat transformers, such as trees that can invade the naturally treeless parts of Galapagos (quinine is one example), other woody species, especially shrubs and climbers (such as the vine Aristolochia or Dutchman's pipe), and some herbaceous species, especially grasses. Up to now, the problem has been worse in the humid highlands of the inhabited islands, but the largest single group of introduced plants is now the ornamentals in gardens, many of which are adapted to semi-arid habitats such as occur in the lowlands of all Galapagos islands, so these may eventually become serious invaders of the relatively pristine semi-arid zone.
Conservation action for invasive plants involves research at five levels:
Source: Charles Darwin Foundation