LEGUMES AND GRASSES AS A BASE TO CHARACTERIZE GRASSLANDS. I. MOUNTAIN PASTURES FROM TERUEL (SPAIN) A stratified sampling was carried out in a large territory, with contrasted ecological characteristics. A balance was made of the plotting of legumes and grasses judging the fitness of only using these plant species in order to classify the grasslands and also for making clear the principal tendencies of biocenotic variation. We were able to verify that this type of sampling enables us to detect a very high number of ecological situatíons, which is in accordance with the variety of species found. The grasses tend to be more localized and in general show a more specified habitat than the legumes. An ordination analysis, with presence-absence data, differenüates well between the communities of acidified soils and hydromorphic pastures; within these it is possible to distinguish different groups whose relative disposition, as a consequence of their floristic affinities, reflects the dynamic relations between community types. The subhumid and xerophytic pastures, that represent 1Q9Í of the inventories, appear undifferentiated in this first stage of the analysis, because of the strong gradient provoked in the ñrst axis by the acid and hydromorphic pastures.

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