Submerged leaf rosette of Nymphoides sp. photographed in Lake Matano by Chris Lukhaup in 2011.
Nymphoides sp. "Lymnocharus"
This plant resembles Ottelia mesenterium in that it also sends its white flowers to the surface on long stalks. But otherwise it is tiny, with rosettes of leaves about 4 cm long. These submerged leaves are fresh green with a flared tip. It also produces the flat floating leaves that accompany the flowers on the surface.
Aquarists call this plant sometimes also "Lymnocharus sp.", but this is not a valid name. It probably comes from Limnocharis flava, aquatic plant originating from Central America and naturalized in southeast Asia which is used in Indonesian cuisine and has somewhat similar leaves, although it is much larger and grows emersed. However, "Lymnocharus" is an aquaristic designation, not a scientific name. It could potentially be Nymphoides parviflora (syn. N. parvifolia), which occurs from India to Australia.
Nymphoides sp. "Lymnocharus" forms loose carpets locally in Malili Lakes (Matano, Mahalona, Towuti). We have seen it in depths between 0,5 and 3 m.
Could be grown in aquarium conditions, but it is very rare.