Phytogeographic Relationships of the Yucatan Peninsula

Abstract

An analysis was carried out to: (a) determine the Similarity Index between the Yucatain Peninsula and adja- cent zones: southern Florida, U.S.A.; Tamaulipas, Tabasco, and Chiapas States, Mexico; Guatemala; Panama'; Cuba, and Jamaica; and (b) establish quantitatively the role played by endemic and antillean elements in the Yucatain flora. Contrary to previous reports, the Yucatain Peninsula is shown to have a greater affinity with northern Central America than with either southern Mexico or the Greater Antilles. The rate of endemism is less than previously cal- culated: 10% instead of the 17% reported by Standley (1930), but it is still significant for a Biotic Province. The proportion of the antillean element with biogeographic rele- vance is 5.4%; also less than formerly reported. In terms of the percentage of total number of species, both the endemic and the antillean elements are relatively unimportant, but in terms of the composition and diversity of the vegetation they are abundant, and sometimes become dominant.