A new seagrass species, Halophila sulawesii, is described in the section Halophila. This species has a similar vegetative appearance as Halophila ovalis (R. Br.) J. D. Hook with the ovate laminae, and has been reported as "deep water H. ovalis" in the literature. However, H. ovalis is a dioecious plant while H. sulawesii is a monoecious one, a feature resembling H. capricorni Larkum, that is the presence of a single male or female flower in separate floral axils of the same rhizome. Both H. sulawesii and H. capricorni have finely serrulated laminal margins however, the laminal surface of the former species is glabrous, while the latter one possesses a few stiff abaxial hairs. H. sulawesii is found on coral sand between 10 to 30 metres and grows adjacent to corals Seriatopora hystrix Dana and Acropora sp. and other seagrasses such as Halophila decipiens Ostenfeld and Halodule uninervis (Forsakal) Ascherson in several reef islands of the Spermonde Archipelago in south-westem Sulawesi, Indonesia. (C) 2007 Elsevier B.V. All rights reserved.