The historical phytogeography is closely related to climatic changes and with the modifications of Ecosystems through time caused by th e p la te tecto nics. This pa lin ostratig rap hic review is the result of the surveys carried out in several sedimentary basin from Baja California to Chiapas, Mexico. The paleochorology of angiosperms in Mexican terrains began in the Lower Cretaceous (Barremian-Aptian) in the northern state of Durango, where at the "Gran Tesoro" appeared jugella sensu Srivastava ( 1994) and Tricolpites cf. T. minutus Brenner, 1963. In the same age, in Michoacán state, southern of Mexico occurred cf. Afropolis (Brenne r) Doyle et al. 1982, at Tepalcatepec Fm. Meanwhile, at the state of Puebla in the Tlayua Fm. (Aptian - Albian), the genus Retimonocolpites Pierce , 1961, as a very scarce palinomorphs in this micrite limestone. During the late Cretaceous a pantropical flora predominated on the continents, and in Mexico three palynological provinces sensu Kedves ( 1985) were recognized: 1) Normapolles province, covering north eastern basins at Coahuila and Tamaulipas with taxa belonging to the Chlorantaceae, Magnoliaceae and to extinct genus Anacolosidites; 2) Aquilapollenites province, found in the occidental part of Mexico at Baja California and Sonora, characterized - besides Aquilapollenites- by the presence of certains paratropical taxa as Gunnera and bombacaceas; 3) Monocolpates province , present at Chiapas with high frequencies of sulcate pollen grains and Proteaceae. In Mexico through the Paleogene -from Baja California to Chiapas- the prevailing flora is pantropical with taxa belonging to the Caesalpinaceae, Bombacaceae, Sapindaceae and Sapotaceae; with a great abundance and diversity of Engelhardtia (Momipiles) together with the presence of boreal and temperate taxa. In the Eocene-Oligocene began the formations of the several types of vegetation, which in mexican territory can be considered two main provinces: one occidental province(Rocky Mountain type) with affinities with western United States and Asia and other eastern province, herein named as the Gulf Coast Province, with more para tropical elements in the northern part and which affinities are with the atlantic flora of Europa and North America (Mississippi embayments); meanwhile in the southern region of this eastern province, there is an increase in the frecuency of neotropical taxa. Finally in the Neogene, the conformation of the present mosaics of vegetations start to build during the Miocene and basically such mosaics continue until the present. Hence, at western Sonora began the establishment of the lower biomass vegetation, in contrast, in the south the neotropical floral start to be present at the coastal plains in the mexican Gulf region; meanwhile at the cordilleras the template and boreal taxa diversified i.e. Quercus and Pinus. Consequently, the mexican flora has a long history since the Early Cretaceous (120 m.a.), where the paleochorology can explain why many taxa that has been considered as neotropical, are indeed pantropical and paratropical relicts which migrated from the North as result of the climate deterioration through the Cenozoic. Other pantropical taxa evolved regionally given rise to other types of vegetation .
Técnicas genéticas en la solución de un problema minero
