The focus of this study was on seed germination and seedling growth of Pterocactus tuberosus, an endemic cactus inhabiting the Monte desert of Argentina, which possesses unusual winged seeds and geophytic habit. We evaluated the effects of water availability, temperature, and light on germination, and the influence of soil moisture on seedling growth. The effects of water potential were examined using 0, −0.1, −0.4, −0.7, and −1.0 MPa solutions. Temperature treatments included 15, 20, 25, 30, 35, 40, 20/10, 25/15, and 30/20 °C. To assess photoblastism, seeds were exposed to light or continuous darkness. Total germination, weighted germination percentages, and mean germination times were calculated. Plant size and biomass of 1- and 6-wk-old seedlings were determined under high, moderate, and low watering frequency treatments. Results showed that decreasing water potential affected germination, which was about 80% at 0 and −0.1 MPa, and then, decreased to almost complete inhibition at ≤ −0.7 MPa. Recovery of germination upon transfer to distilled water was successful, thus, suggesting that seeds maintain viability after exposure to reduced water potential. Seeds germinated under constant and fluctuating temperatures in the 15–35 °C range, with higher values between 20 °C and 35 °C, and marked inhibition at 15 °C and 40 °C. Germination occurred in darkness (58%) but was enhanced by light (84%). Both 1- and 6-wk-old seedlings grew substantially larger under high water availability but reduced their growth as the extent of the dry period increased. Similar proportion of biomass was allocated to roots and aerial parts, regardless of watering treatments, suggesting the relevance of the tuberous root as a water-storage organ. It appears that this root system may contribute to seedlings’ ability to withstand drought.