Palms

Palms are widely distributed throughout moist tropical and subtropical regions of the world. They can be found in steamy rain forests, deserts, mangrove swamps, and high mountain thickets. Palms are uncommon in hot, dry regions, however, occurring only where there is a constant source of underground water. The distribution of palms in the tropics is uneven. The greatest diversity of palms is in the eastern tropics of Indo-Malaysia, the Guianas, and Brazil. Africa has relatively few palms with only 16 genera and 116 species; there are fewer palms in all of Africa than on the island of Singapore. The low diversity of palms in Africa is attributed to the dryness of much of the continent.

Palm species are also unequally distributed taxonomically among genera. A small number of genera contain a disproportionately large percentage of palm species. The genus Calamus is the largest with about 400 species in the Old World tropics. In the New World, Chamaedorea is a large genus with about 100 species in southern Mexico, Central America and northern South America. The average number of species per genus is relatively small at 13 and more than half of all the genera have five or fewer species. Seventy-three of the 212 genera of palms consist of only one species that is geographically restricted to a small area, often on an island. The palm floras of the New and Old Worlds are on the whole quite dissimilar.

Very few palms occur in temperate regions. In Europe, for example, there are only two native palms: the dwarf fan-palm (Chamaerops humilis), which is found in dry sandy and rocky places along parts of the Mediterranean coast, reaching the latitude 44°N, and the Cretan palm (Phoenix theophrasti), which is an extremely rare palm found only on the eastern side of Crete. In the Himalayas at 32°N, the palm Trachycarpus reaches an altitude of 7,875 ft (2,400 m) where snow lasts from November to March. In North America, the genus Coconut palms in Florida. JLM Visuals. Reproduced by permission.
Serenoa, which includes the palmettoes of the southeastern states, reaches 30°N. The scarcity of palms in temperate regions where frosts occur is likely related to their mode of growth. Palms generally have only one growing point which is at the tip of the stem or trunk. If this single bud is killed, then the palm dies. It appears that in the vast majority of palms, the growing tip is highly sensitive to frost and that few species have been able to overcome this sensitivity.