Endemic species of grasses in Mexico:: a phytogeographic approach

The Poaceae family includes approximately 700 genera and 10 000 species, and Mexico is considered one of its most important centers of diversity and endemism. A total of 256 taxa (including 16 subspecific taxonomic units), belonging to 65 genera, are endemic to Mexico. Some of them are close relatives of important crops, while others are used in different ways all over the country. The aim of this paper is to discuss the distribution patterns at state level of the Mexican endemic species of Poaceae. Using cluster strategies, the states are classified according to their floristic similarities. Later, hotspots of endemism are identified, in order to discuss their role in conservation strategies. To evaluate the importance of each state in the conservation of the Mexican endemic Poaceae, two iterative complementarity methods were also used. Our results show that the largest concentration of endemic taxa occurs in a few states, such as Jalisco, Mexico, Michoacan, Durango, Oaxaca, Veracruz, San Luis Potosi, Chiapas, Chihuahua, Puebla, and Coahuila. The results also show that there are some patterns in the relationship to its endemism that seem to reflect important diversification trends in the family. Accordingly, 31% of the grass genera of Mexico have at least one endemic species, and 16.7% of the genera have only one endemic species. In contrast, six genera contribute 47.2% of the total number of grass endemics in Mexico. The Chloridoideae contributes 42.9% of the total grass endemic species of Mexico, whereas the Panicoideae includes 24.6%, and the Pooideae 19.8%. Thus, these three subfamilies contribute about 87% of the species endemism. On the basis of the habitat and distribution patterns of these subfamilies, two main areas of endemicity can be identified. The first area is located in warm habitats, whereas the second is related to temperate and high regions. The cluster analyses indicate the occurrence of four state groups whose phytogeographical explanation is discussed on the basis of a floristic regionalization of Mexico. The results also indicate the need to establish a relatively high number of sites and states for the conservation of 256 endemic taxa. The elevated number of sites required to conserve the Mexican endemic Poaceae is mainly due to the fact that many taxa have a restricted distribution pattern. On the basis of the patterns obtained, a few proposals are presented for undertaking the establishment of conservation priorities of these taxa.