Rzedowski, Jerzy
June 1991
Acta Botanica Mexicana;jun1991, Issue 14, p3
Academic Journal
The phanerogamic flora of Mexico is estimated at roughly 220 families, 2410 genera and 22000 species. The highest incidence of diversity is found along a belt which originates in Chiapas, traverses Oaxaca, continues to central Veracruz on one side and to Sinaloa and Durango on the other. Cloud and tropical evergreen forests are the most diverse per unit area; however, in absolute numbers of species, other vegetation types surpass them. Approximately 10% of the genera and 52% of the species are endemic to Mexico. These figures rise to 17% and 72% respectively if an ecologically more natural area is considered as the point of reference, although this would extend the area of Mexico by about one-third. Endemism is most pronounced in the xerophilous scrubs and in the grasslands, and at the species level it is also high in other types of vegetation, with the exception of the evergreen tropical forests. The above figures indicate that the country has been the site of origin and evolution of a great number of plant lineages: a) in the arid and semi arid zones of northern Mexico plants have experienced intense evolution, giving way to a moderately rich and distinctive flora with specialized growth forms which are often unique; b) the flora in the semi-humid regions developed largely from elements which exist in other parts of the world; a considerable number of these elements has led locally to extensive secondary radiation resulting in an abundant and diverse flora; c) the flora of the humid areas, especially of the warm-humid areas in the east and southeast of the country is also quite varied; yet to date, there is not much evidence that Mexico could have been an important center in its evolution. An analysis of the geographical affinities of the phanerogamic flora of Mexico indicates that its links with the south are about four times more important that those with the north. This fact should not, however, be interpreted as meaning that such a large majority of Mexican plants derived directly from the south, since a good number of elements common to Central and South America must have originated in Mexico or in other parts of the world, such as the Antilles, Africa, Eurasia and North America. Available fossil records show that the basic features of Mexican present phanerogamic flora were already well established by the mid-Tertiary or earlier.


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