Galápagos tomato  (Solanum cheesmaniae)

This species has not yet been assessed by the IUCN (1).

Solanum cheesmaniae is one of two wild tomato species endemic to the Galapagos archipelago (2). Having evolved in isolation from mainland tomato species, it exhibits a range of unusual characteristics, such as bright orange-yellow fruit, yellow-green foliage and minute seeds (3). Although it initially grows upwards, mature plants often spread along the ground, with the hairy stems branching profusely (4) (5). The spear-shaped leaves are relatively small, fleshy and sticky, while the yellow flowers are covered in hairs like the rest of the plant (6) (7). It is morphologically quite variable across the archipelago, but owing to a strong dependence on self-pollination, individuals within each population are strikingly uniform in appearance (6). Until relatively recently, the only other endemic wild tomato species, S. galapagense, was considered a subspecies of S. cheesmaniae, but is now treated as a separate species (2) (4).

Endemic to the Galapagos Islands where it occurs on several of the major islands and smaller islets (2).

Owing to high salt tolerance, S. cheesmaniae is able to thrive on coastal lava flows within close range of the sea, but also grows on slopes up to 1,300 metres above sea level (2) (3) (4).

S. cheesmaniae flowers and fruits throughout the year, but exhibits a flowering peak at the beginning of the Austral winter, between April and June (4). Although the flowers are structured in a way that favours self-pollination, some cross-pollination is thought to be likely, with the native Galápagos bee (Xylocopa darwinii) being a possibly pollinator (2) (3). Passage through the gut of a giant tortoise was originally thought to be a requisite for seed germination (6), but recent evidence suggests this may not be entirely true, particularly given that S. cheesmaniae occurs on islands that possibly never had a tortoise population (2).

Human activity and introduced animals, such as feral donkeys and goats, threaten many S. cheesmaniae populations. In addition, introduced tomato species have the potential to genetically contaminate the endemic species through interbreeding (2) (3).

The endemic Galapagos tomatoes are considered to be of great value to the breeding of the cultivated tomato, and consequently of great conservation significance. It is currently thought that the best means of conserving the endemic species is to establish protected reserves that exclude introduced herbivores and are free from introduced plants (2) (3).

For further information on the conservation of the endemic flora of the Galapagos see:

• The Charles Darwin Foundation:
  www.darwinfoundation.org
• Galapagos Conservation Trust:
  http://www.gct.org