ON THE ALIEN FLORA OF THE PROVINCE OF BUENOS-AIRES, ARGENTINA

The province of Buenos Aires is situated on the eastern side of central Argentina. Its area is 307 563 km2 and it extends westward from the coast of the Atlantic Ocean for ca. 600 km. The topography mainly consists of pampa, which today is in agricultural use. During four journeys lasting altogether ca. six months in 1967, 1974, 1978 and 1983, I had the opportunity to study the flora of Argentina, of which alien immigrants form a considerable part, particularly in the capital Buenos Aires and its surroundings. This paper lists after the continent of origin all the alien species reported in the floras evidenced as found in the province of Buenos Aires. These number 404, making up 23.4% of the total 1 730 species of the province. Europe has contributed 337 species (83.5% of the aliens), Africa 23 (5.7%), Asia 21 (5.2%), North America 20 (5.0%) and Australia and New Zealand 3 (0.7%). The frequency of the aliens in the province is estimated on a scale from 1 to 5. All the 29 species in the highest category 5 are of European origin, and only four of the 66 species in category 4 are from outside Europe. The aliens have often proved superior to the indigenous species in a cultivated environment, and many of them have intruded into more or less natural vegetation, too, e.g. pastureland, marshes, coastal dunes and the forest belt along the Atlantic shore. The role of horses and cattle in dissemination and the status of aliens is discussed.