Recent molecular evidence supports the transfer of two Australian endemic species, Austrocynoglossum latifolium (R.Br.) R.R.Mill and Cynoglossum suaveolens R.Br., to the genus Hackelia Opiz as H. latifolia (R.R.Mill) Dimon & M.A.M.Renner, comb. nov., and H. suaveolens (R.Br.) Dimon & M.A.M.Renner, comb. nov. Hackelia latifolia comprises two morphological entities that, although sharing the procumbent-prostrate habit and production of elongated internodes and frondose bracts in the inflorescence, differ in a range of qualitative and quantitative micro-morphological characters. Hackelia latifolia has few, widely spaced, thorn-like trichomes on stems, a glabrous abaxial lamina surface, and mericarps with free glochids densely and evenly distributed over the outer surface, and a rectangular cicatrix at the mericarp apex, which is beaked. The other entity has many densely packed cellular trichomes on the stems, trichomes on the abaxial leaf lamina, and mericarps with a wing formed by basally connate glochids, and a triangular cicatrix located centrally on the inner mericarp surface. For the latter, we propose the new species Cynoglossum torvum Dimon & M.A.M.Renner, and by implication suggest that H. latifolia is polyphyletic as previously circumscribed. Whereas H. latifolia s.s. is widespread along the south-eastern coast of Australia from Tasmania to south-eastern Queensland, Cynoglossum torvum is restricted to the tablelands of north-eastern New South Wales and south-eastern Queensland. We compare C. torvum with the other Australian Cynoglossum L. species, C. australe R.Br., confirm previous observations of variation in mericarp morphology, and suggest that further investigation to resolve species circumscription is required given this variation.