Floristic Richness and Endemism in Mexico

The fact that Mexico together with Central America constitutes one of  the regions of greatest plant diversity, has long been known. The task of quantifying the diversity of Mexican flora, however, has been slowed down by lack of comprehensive inventory of known species and also due to the estimated significant number of undiscovered species.
Today the knowledge of floristic richness keeps on growing revealing many interesting facts.

The distribution of plant biodiversity within Mexico is not (as expected) even. The states with the highest concentrations of species are Chiapas, Oaxaca and Veracruz. A significantly lower number of species can be found on the Yucatán Peninsula, which includes the states of Yucatán, Quintana Roo and Campeche (see map).

Floristic Diversity in Mexico
It is also interesting to note, that six plant families make up around 40% of Mexican flora and that the relative importance of each family varies from region to region. Compositae, Gramineae and Cactaceae are best represented in the northern and central parts of the country, whereas Orchidaceae and Rubiaceae are more diverse in the southern half. Leguminosae become more abundant in warmer climates.

The flora of Mexico is also notable for its large number of endemics. It was estimated that 12% of world's genera are restricted (endemic) to Mexico, which represents one of the highest percentages of generic endemism in the world. Thus with a flora of 20,000 to 30,000 species, 10,000 to 15,000 may live only in Mexico.The highest plant endemism at the species level is to be found in temperate and subhumid montane highlands (70%) and arid and semi-arid areas (60%), moderately high (40%) in subhumid tropical areas, moderate (30%) in humid temperate areas and low (5%) in humid tropical lowlands. The reasons for such a biological wealth are many.
Read about them in the Mexican Biodiversity section.

A remarkable correlation can be observed between high endemism at the levels of genera and species and strong climatic aridity. At the species level, temperate and semi-humid areas are equally endowed with endemics. However in warm humid regions, endemism is poor. In general, endemic genera are better represented in the northern half of the country, and endemic species are more numerous on the Pacific slopes than the Atlantic slopes.
source: Centers of Plant Diversity - The Americas
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