The relative allocation of biomass within monospecific stands of Acaena magellanica that vary in level of wind and water stress differ greatly. Populations in January 1983 varied in leaf biomass from 192 to 2373 g wet wt m-2 (1105 to 10023 kJ m-2) Inflorescences were not produced at either of these extremes of leaf biomass. In two populations with intermediate levels of leaf biomass (597 and 640 g wet wt m-2, 3185 and 2664 kJ m-2), inflorescent biomass was 104 and 273 g wet wt m-2 (385 and 1127 kJ m-2). The relative allocation to sexual reproduction is thus not constant in A. magellanica. The levels of energy in the leaves and inflorescences did not differ greatly despite differences in proximate composition. © 1989 Springer-Verlag.