Seed reproduction is considered a critical bottleneck of the plant life cycle, constraining population growth, especially in the Mediterranean area. In this study, we investigated seed reproduction of Lamyropsis microcephala (Asteraceae), a threatened species occurring only in the Gennargentu massif (CE Sardinia, Italy). Seed output was quantified in two of the four localities where the species occurs, which differed in population size. Germination of seeds from all the four localities was assessed, both in the field and under controlled conditions, and the annual trend of soil temperature recorded by data-loggers. Plants had ca. 60 cypselas (i.e. the fruits of Asteraceae) per capitulum in the larger Rio Aratu and ca. 30 in the smaller Pisargiu locality, with only ca. 1.7 and 0.3 germinating cypselas per capitulum, respectively. Under controlled conditions, seeds of the two large localities (Bau 'e Laccos and Rio Aratu) germinated above 80%, while those of the two small ones (Bruncu Spina and Pisargiu) did not reach 55%. All seeds sown in the field germinated in April June, when diurnal fluctuations of temperatures were almost 10 times higher than in winter, limiting the length of the growing season before the onset of summer drought, and highlighting an increasing threat from global warming.