The taxonomic status of Myriophyllum callitrichoides Orch. in Western Australia is reviewed. On the basis of new collections made across the Kimberley, a previously unknown taxon with unique mericarp ornamentation is documented, here described as the new species Myriophyllum foveacola M.D.Barrett, M.L.Moody & R.L.Barrett. M. foveacola deserves the same rank as the two previously described subspecies, however we prefer to treat them at the rank of species. Myriophyllum striatocarpum M.D.Barrett, M.L.Moody & R.L.Barrett nom. nov. is elevated to species rank from the previously recognised M. callitrichoides subsp. striatum Orchard (non M. striatum Orchard). Both species are endemic to the Kimberley region of Western Australia. The three species now recognised in the M. callitrichoides complex have morphological, ecological and / or geographic distribution to support their status as species. The two Western Australian species are of conservation significance in Western Australia. Illustrations are provided for both of the Kimberley species.