Ruppia maritima
Description
Submerged annuals (rarely perennial) with a reduced rhizome;
Leaves up to 15 cm long, usually not longer than 10 cm, and 0.5-1 mm wide, light green;
Inflorescence pedunculate.
Flowers 2, with 2 stamens and usually 4 subsessile carpels each.
Fruits ovoid, asymmetric, rather swollen;
Distribution
Asia-Tropical: Philippines (Philippines present), Lombok present, Madura present, Peninsular Malaya present
The species has a worldwide distribution, in the north as well as the south temperate zone and in the tropics, in brackish water and in continental salt lakes. The distribution of the species in Malesia is poorly known. It has been recorded from Peninsular Malaya and the Philippines. Wood & Baas Becking () record the occurrence of extensive beds of R. maritima var. spiralis in healthy condition in waters with a salinity of 6% and a temperature of 30 °C on Madura. Recently it was collected on Lombok.
Ecology
In shallow, standing brackish water it may form dense beds, without other aquatic plants. According to McCann () aquatic birds are largely responsible for the dispersal of the seeds of Ruppia; indeed, young flamingoes seem very dependent on the seeds as a food source, but as these birds do not migrate their role as agents of dispersal is doubtful; moreover, it has not been checked whether some seeds are actually passing the intestinal tract unharmed.
Morphology
In Malesia some variation has been observed in the Ruppia material. Ridley, l.c., mentioned specimens from Wellesley, Peninsular Malaya, which had straight peduncles with a length of 1-6 inches; this is outside the normal range of peduncle length in this species, but would fit R. maritima var. longipes Hagstr. The latter variety has been described from Central Asia (Buchara), and has been found in southern Spain and the east coast of North America; it may turn out to be a proper species. The record of Wood & Baas Becking, l.c., of R. maritima var. spiralis Koch (material not seen) from Madura may also relate to another taxon.