This study provides the first comprehensive evaluation of the population of Coscinodon horridus (J.Muñoz & H.Hespanhol) Hugonnot, R.D.Porley & Ignatov in France, a recently discovered species in Meygal (Haute-Loire). A total of 876 individuals (one cushion = one individual) were recorded amongst lava scree on three sucs (volcanic summits), of which 99.6% occur on a single summit. The detailed population counts provide an accurate base-line for future monitoring. Male plants are very rare and the sex-ratio is strongly biased towards females. Sporophytes are also very rare. Coscinodon horridus is a mountain species, strongly linked to harsh environments, mostly on steep exposed slopes of south–east aspect yet is predominately associated with sheltered niches that are protected from direct precipitation and insolation. Sheltered individuals tend to be vegetatively more robust than those growing in more exposed situations. The unique hairpoint anatomy of C. horridus, complex water relations and competitive interactions may explain the narrow niche that this species occupies. Due to the very small area of occupation in France and the low number of individuals, Coscinodon horridus is considered to be threatened in France and is classified as Endangered.