Ephemeroid plants in Junggar Basin were studied to understand how they allocate biomass and grow. Three Sterigmostemum species were compared, showing differences in organ biomass and allocation ratios. S. fuhaiense had the most biomass but lower root and leaf ratios. S. tomentosum had the least biomass but the highest leaf ratio. S. sulfureum had the highest root ratio. As plants grew, the root to shoot ratio decreased. S. fuhaiense had isometric biomass allocation, while the others showed allometric effects. All species had a common allometric scaling exponent for leaf to belowground biomass. In conclusion, the three species had different biomass allocation patterns, but they all represented the characteristics of ephemeroid plants.