Hymenachne amplexicaulis (capybara grass) has been listed among Australia’s 20 worst weeds (or weeds of national significance) but has not been officially recognised as a target for biological control. Nevertheless, collections are being made of fungal pathogens associated with this amphibious grassy weed and of other aquatic weeds native to Brazil. This paper represents the second contribution towards the description of the pathogenic mycobiota of H. amplexicaulis in Brazil. Two new fungal records are described and illustrated: Passalora barretoana stat. et comb. nov. and Paraphaeosphaeria michotii. The latter is described in association with its anamorph, which belongs to the genus Microsphaeropsis. The status of the taxon Phyllachora sp., recorded in a previous publication, is elucidated and a more complete description is provided here.