A new genus and two new species are described and compared with related algae. All were isolated from terrestrial habitats on Signy Island, South Orkney Islands, Antarctica. They are Signiosphaera multinucleata gen. et sp. nov. (Tetrasporales, Chlorophyceae), Chlamydocapsa lobata sp. nov. (Tetrasporales, Chlorophyceae) and Chloromonas palmelloides sp. nov. (Volvocales, Chlorophyceae).