A systematic revision of Gnidia L. is presented based on an analysis of morphological data. The circumscription of the genus adopted here includes Lasiosiphon Fresen. and excludes Atemnosiphon Leandri and Dais L. Six new combinations are made for species previously recognized as Lasiosiphon: G. ambondrombensis (Boiteau) Z. S. Rogers, G. hibbertioides (S. Moore) Z. S. Rogers, G. humbertii (Leandri) Z. S. Rogers, G. linearis (Leandri) Z. S. Rogers, G. occidentalis (Leandri) Z. S. Rogers, and G. perrieri (Leandri) Z. S. Rogers. Two names, G. daphnifolia L. f. and G. linearis, are resurrected from synonymy with L. madagascariensis (Lam.) Decne. and L. decaryi Leandri, respectively, and now pertain to more broadly circumscribed species. One new species, G. neglecta Z. S. Rogers, is described. These changes result in the recognition of 14 species, all endemic, making Gnidia the largest genus of Malagasy Thymelaeaceae. Lectotypifications are provided for 15 names: Dais gnidioides Baker, G. danguyana Leandri, L. bojerianus Decne., L. decaryi, L. decaryi var. erectus Leandri, L. decaryi var. littoralis Leandri, L. decaryi var. tenerifolia Leandri, L. dumetorum Leandri, L. hildebrandtii Scott-Elliot, L. humbertii Leandri, L. madagascariensis var. angustifolius Leandri, L. madagascariensis var. mandrarensis Leandri, L. occidentalis Leandri, L. perrieri Leandri, and L. pubescens (Lam.) Decne. var. multifolius Leandri. Each species is illustrated, mapped, and assigned a preliminary IUCN conservation status.