Shoot and root development as well as the flowering of two desert species of the bulbous genus Bellevalia (Liliaceae) were studied in the field and under different temperature and air and soil humidity regimes. In B. eigii, foliage leaves and inflorescences of the new shoot are already visible within the bulb in September. In B. desertorum, inflorescences only start to develop around November. In all the other life-cycle transitions studied, B. desertorum is faster than B. eigii, as shown by the development of roots and shoots within and outside the bulb until above-ground shoot emergence and by the development of the flowers from bud appearance within the bulb to anthesis, both in response to increased moisture conditions. The first stages of root development take place also under dry conditions in B. desertorum, but not in B. eigii. Shoot development appears to depend on root development. Flowering in B. desertorum, which takes place around December- January, is delayed for up to 1.5 weeks by lower soil water availability, while B. eigii flowers in February-March even under low water availability. The faster responses in B. desertorum coincide with its shallow bulb depth and its occurrence in more arid habitats (south-facing slopes) and open sites in wadis in the Central Negev Highlands, in contrast to the deep-rooted B. eigii, which occurs in the Central Negev Highlands only in broad loessial wadis and loessial plains.