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The fitogeographic areas from the tucumano-boliviano forest (BIB) from Argentina and Bolivia and the temperate austral forest (BTA) from Argentina and Chile are separated by de arid diagonal (approximately by 2,000 km between forests). The objective of this work is to know how many genera with species of arboreal habits are distributed in the temperal austral and tucumano-boliviano forests. In this work, the genera with species of arboreal habits distributed in each forest are analyzed and compared. In addition, the biogeographic element for each genus is shown. 125 and 29 genera were detected in BIB and in BTA respectively, and the remaining 13 genera were present in both forests. The total 167 genera were distributed in eight biogeographic elements. The most abundant elements were the neotropical and pantropical, followed by the austral and temperate forest endemic. The first ones were more frequent in the BIB, while the other two elements were more frequent in the BTA. The genera shared by both forests corresponded to the austral, neotropical, pantropical, and holartic elements. From these shared genera, different hypotheses to explain the disjunction are postulated. One hypothesis is that they may have distributed widely in ancient times and that the geoclimatic conditions caused the disjunction. Another hypothesis is that long distance dispersal events occurred after the formation of the arid diagonal. Restricted BTA genera would suggest relictual status of an ancient origin in Gondwanaland, while restricted BTB genera would be products of various relatively local diversifications.