Soil salinisation and alkalisation constitute major constraints to agricultural productivity and ecosystem rehabilitation in arid regions, where secondary salinisation is exacerbated by suboptimal irrigation practices. Halophytic species within represent valuable models for investigating plant adaptation mechanisms to saline-alkaline stress. However, knowledge gaps persist regarding congeneric species' differential responses to specific salt types and their synergistic effects, limiting informed species selection for ecological restoration in heterogeneous saline environments. This comparative study examined two perennial congeners - - Limonium aureum and Limonium bicolor - from Minqin County, China, through controlled experiments simulating three stress regimes: sodium chloride-dominated salinity, sodium bicarbonate-driven alkalinity, and combined saline-alkaline stress using 1:1 sodium chloride to sodium bicarbonate mixtures across concentration gradients. Three key findings emerged: (1) Germination parameters (rate, potential, index) exhibited concentration-dependent declines across all treatments, with species-specific tolerances - The superior sodium chloride resilience of Limonium bicolor (89.82% semi-lethal concentration) contrasted with the enhanced sodium bicarbonate tolerance of Limonium aureum (21.96% semi-lethal concentration). (2) Seedling growth displayed biphasic responses to sodium chloride (stimulatory at concentrations <= 100 millimolar, inhibitory above 100 millimolar) but monotonic decline under alkalinity and combined saline-alkaline stresses, accompanied by increased root-to-shoot ratios across treatments. (3) Principal component analysis revealed differential stress sensitivities: Limonium aureum shoot elongation was most sensitive to combined saline-alkaline stress (PCA 1 loading = 0.92), while Limonium bicolor biomass accumulation showed greatest vulnerability to combined saline-alkaline stress (PCA 1 loading = 0.87). These results establish a physiological basis for ecological deployment strategies: The superior sodium chloride tolerance of Limonium bicolor makes it suitable for chloride-dominated soils, while the bicarbonate resilience of Limonium aureum renders it ideal for alkaline substrates. Their complementary stress adaptations highlight the value of conspecific selection in heterogeneous saline landscapes. This study provides the first quantitative comparison of congeneric halophytes' stress thresholds under combined saline-alkaline conditions, advancing our understanding of Plumbaginaceae adaptation mechanisms while offering practical guidelines for desert ecosystem restoration.