Here, we report the results of a study of the genotypic variability in phenology, morphology and other characteristics of 34 accessions of Medicago polymorpha collected along a rainfall gradient in the Mediterranean zone of Chile in 1988, between La Serena (290 55' S; 100 mm mean annual rainfall) and Temuco (380 47' S; 1,400 mm). In raised beds, a total of 44 seeds were sown for each accession in two 1.1 m rows, with 20 cm between rows and 5 cm between seeds within a row. Three distinct phenophases were identified: flowering, onset of fruiting, and senescent. Morphological characterization of plants seed and pods was also carried out, comparing biomass productivity, seed production per plant, number and weight of seed per pod, and seed hardness as revealed by germination tests. Life span in the accessions studied never exceeded 170 days. Northern accessions, from the arid region, were the earliest flowering, but least productive in terms of overall biomass production. Conversely, the late-flowering accessions were significantly more productive ofbiomass. Additionally, an unusually high proportion of the accessions with spiny seed pods occurred in the south. The ecological and agronomic implications of these results are briefly discussed.