Island Flora

the plant life of an isolated area of dry land. The more or less distinctive species composition of island flora is determined by the degree of isolation of the island and by the length of time the island has existed. It is also determined by the specific conditions surrounding the flora’s development.

As a rule, islands have fewer species than do continental areas of equal size. The most meager floras are found on young oceanic islands, such as the tropical coral islands of the Pacific. The floras of continental islands usually are quite distinctive and are noted for the richness of their species composition. The comparatively few species that make up the flora of the Galápagos Islands, the Juan Fernández Islands, the Mascarene Islands, St. Helena, and Ascension Island are distinctive and include a significant number of endemics, thus indicating the length of their isolated development.

The floras of old continental islands, such as New Zealand, New Caledonia, and Hawaii, are unique, reflecting the diversity of natural conditions and the completeness and long duration of isolation. The ancient forms of such island floras have been enriched by the formation of young species under conditions of prolonged isolation. Endemics are abundant, making up as much as 70 to 80 percent of the species composition. Endemism is less strongly expressed on islands that are not situated far from the mainland, such as Japan, Sri Lanka, and the Canary Islands.

The floras of such large continental islands as Indonesia and the Philippines often consist of as many species as those of the mainland but usually exhibit greater endemism. The kinship of island and continental floras reflects both modern and ancient relationships between the dry land and the sea. In addition, the directions of plant migrations in past epochs is reflected. (For example, the flora of the Hawaiian Islands, which lie closer to North America than to Asia, resembles the tropical floras of the Old World.)