POSIBLE SIGNIFICACION DEL PORCENTAJE DE GENEROS BICONTINENTALES EN AMERICA TROPICAL (Afinidades de la flora arbórea de regiones húmedas del sureste de México)

Resumen

It was of interest to define the floristic and vegetative relationships of the humid zones of southeastern Mexico. In order to do this on a comparative basis, no complete floras were used. Instead, a comparison was made between the dominant arboreal genera in the evergreen rain forests, formations characteristic of the humid
tropical regions. In addition, the comparison included two types of temperate forests, one from the north (Tennessee), and the other from the south (Valdivia, Chile) and also the arboreal genera with tropical affinities from two fossil floras (Chalk Bluffs, and Wilcox) well-known in North America.
The results of the comparative analysis seem to be sufficiently coherent to suggest that the method used approaches the correct one.
The following characteristics have been used to define the phytogeographical nature of the floras studied:
A. Percentage of arboreal genera with a bicontinental distribution, that is, with a distribution extending beyond the american continent.

B. Differences in the percentages obtained between the bicontinental and non-bicontinental genera when a local association is compared with the regional formation of which it is a part.
C. Percentage of arboreal genera from the various floras outside Mexico, which are also found in southeastern Mexico.
D. Ratio between the number of bicontinental genera found in Asia and America, and the number of those found in Africa and America; also, a study is made of the percentages obtained by dividing the first and second of these groups by the total of bicontinental genera.
The results of the comparative study are presented in the graphs.