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The germination behaviour of two Iberian endemic labiates, Sideritis pungens and S. chamaedryfolia selected from different habitats, ranging from very humid to semi-arid, was studied under controlled experimental conditions. A factorial experiment, combining different temperature regimes (10 degrees, 15 degrees, 20 degrees, 25 degrees or 30 degrees C), photoperiod (total darkness and 12 h light/12 h darkness) and different pre-treatments (freezing, dry-heat, hot-water), was designed to analyze seed germination patterns and dormancy processes. The. results obtained are in agreement with the ecology of the two species. Seeds are not dormant after collection and maintain high viability when preserved by standard seed bank conservation protocols. It was found out that optimal temperature for germination is 20 degrees C for both species. Light seems to play a key role in the germination of genus Sideritis, particularly for S. chamaedryfolia, significantly inhibited by light as other psammophilous plants. Temperature and light arc relevant environmental indicators, but it was found out that the germination response to these factors in the studied species is correlated with a different environmental factor, namely the availability of water resources in their habitats, which is generally a major constraint factor for seed germination in Mediterranean areas. The results indicate that germination limitations are not so much related to taxonomic position, but rather adaptations to water restrictions.