Sempervivum funckii var. aqualiense, considered the only endemic vascular plant taxon of Belgium still existing in the wild, is threatened by urban development. There is a need for proposing appropriate in situ or ex situ conservation strategies through a precise evaluation of population demographic and genetic characteristics. We investigated demographic dynamics for six years (rosette density, floral production, reproductive success, seed germination and seedling recruitment), pollination (visiting insects and potential pollinators) and genetic diversity using ISSR markers of the unique population of S. funckii var. aqualiense. Visiting insects and potential pollinators, especially common and generalist pollen foraging bees, are abundant in the population of S. funckii var. aqualiense and the plant seems highly attractive. Pollination limitation does not represent a conservation issue. Despite a good floral production in most years (250–1,558 flowering ramets, comprising 4–36 flowers), viable seed production and germination represent very rare events (0.05% viable seeds and 1 seedling) because of meiosis abnormalities related to the hybrid origin of the taxon. Recruitment by clonal propagation (vegetative rosettes) has been detected. Genetic diversity is very low (H = 0.0148), and may have originated from somatic mutations, related to extensive vegetative propagation, but is also compatible with relictual segregating sexual reproduction. Conclusions – The most cost-effective method for establishing new populations is the transplantation of rosettes. Given the low viable seed production, creating an ex situ seed bank requires collecting seeds for many nonconsecutive years. Conserving the rare genotypes can be done by preserving seeds and as many rosettes as possible. The preservation of the only existing population in its entirety appears to be the best option for long-term sustainable conservation of S. funckii var. aqualiense, and any partial destruction of the population should be avoided.