Two new trigger plants from south-west Western Australia, Stylidium perula Wege and Stylidium thylax Wege, are described and illustrated. Revised descriptions are provided for the morphologically allied S. sacculatum F.L.Erickson & J.H.Willis and S. pseudosacculatum Lowrie, A.H. Burb. & Kenneally. Features of trichome structure are argued to provide important taxonomic characters at the species level in Stylidium. The morphology and function of the column cunabulum is explored.