Tephroseris longifolia subsp. moravica (Asteraceae) is an endangered narrow endemic taxon recently recorded from nine sites in Slovakia and the Czech Republic. We provide the first consistent information on its reproductive biology – mating system, seed output, germination, seedling emergence and survival. Based on results from isolation, hybridization and emasculation experiments on different subspecies, T. longifolia s.l. should be treated as an allogamous taxon without apomictic reproduction. Five populations of T. l. moravica were studied in detail for seed output and germination characteristics. The output of well-developed seeds per flowering shoot was estimated to be 592 (1125 seeds per flowering plant). A granivorous butterfly, Phycitodes albatella (family Pyralidae), was identified as a pest, reducing seed output by 18–28%. Germination (reaching 30–62% after dry storage for 4 months) rapidly decreased with storage in room conditions. Deep freeze storage increased germination, although not significantly. Seeds obtained from natural populations had higher germination percentages and germinated faster than seeds from cultivated plants. Seedling emergence in situ was very low (0.9–2.06% of the sown seeds) without significant differences among sites.