The phylogenetic placement of Monocarpus sphaerocarpus D.J.Carr (Monocarpaceae), a member of the complex thalloid liverworts with highly specialised morphology, presumably related to its saltpan habitat, has been determined on the basis of molecular data. Within the complex thalloid liverworts, Monocarpus resolves as sister to the Sphaerocarpales clade. A new line drawing of Monocarpus is provided, as are the first colour photographs of living plants. Detailed ornamentation of the spores of Monocarpus collections from Australia and South Africa, as revealed by scanning electron micrography, is reported, and some of the morphological features that unite and separate Monocarpus and the Sphaerocarpales s.str. are discussed.