Patterns of resource allocation were investigated to analyze variations in adaptive mechanisms in 54 strains of the complex Oryza perennis, which exhibited a perennial-annual continuum. The proportion of seed weight to total dry weight, an indication of reproductive effort, ranged from near 0% in some perennials to 50% in some Asian wild annual strains and in cultivars of O. sativa which were tested for comparison. In general, annual strains allocated more energy to the production of seeds and awns. while perennial strains allocated more energy to the production of vegetative organs and anthers. Patterns of resource allocation were associated with various life history characteristics that affect breeding systems and stress tolerances. Allocation patterns must be the products of natural selection in different habitats, and such selection must have given rise to genetic differentiation of this complex species into forms with varying adaptive strategies.