Nassauvia falklandica (Compositae: Mutisieae: Nassauviinae), a new endemic herbaceous sub-shrub from the Falkland Islands, is described, illustrated and its conservation status assessed. N. falklandica is unique within the genus in possessing a row of pits towards the apex of the abaxial surface of its leaves; stomata and stiff white hairs are confined to these pits. This adaptation most likely reduces water loss in the sparsely vegetated feldmark habitats exposed to strong and drying winds in which it occurs. Its apparent restricted habitat preference contrasts in particular to the wide distribution of one of the other two Falkland endemic Nassauvia species, N. gaudichaudii. N. falklandica has an estimated world population of fewer than 250 mature individuals and is currently only known from two sites on West Falkland c. 34 km apart. Both sites are located on hill summits between 400 and 500 m altitude. The subpopulations are severely fragmented and at risk from genetic erosion, damage by livestock and stochastic events. N. falklandica is assessed as Critically Endangered B1ab(iii), B2ab(iii).