A new scale-leaved trigger plant with conservation priority, Stylidium diplotrichum Wege, is described and illustrated. Revised taxonomic descriptions and notes are also provided for the priority species S. pseudohirsutum Mildbr. and S. expeditionis Carlquist, and the more commonly occurring S. hirsutum R.Br. and S. crossocephalum F.Muell. Leaf anatomy data are provided for all species. The location of the stomata is shown to be taxonomically informative.