Ottelia is a genus of submerged and emergent aquatic herbs in the family Hydrocharitaceae (order Alismatales), first described as a genus in 1805. It is the second-largest genus in its family and comprises plants native to tropical and subtropical regions across Africa, Asia, Australia, New Caledonia, and Brazil.
Plants in this genus are highly variable in form but share a characteristic body plan: crowded leaves borne on short or elongated stems, with some leaves floating at the water surface on long petioles. The rooting stem is elongated. Flowers are enclosed within a herbaceous, many-nerved bract (spathe) that is shortly divided into two lobes. Each flower has two whorls of a trimerous perianth held above the beak of the ovary — a stiff, oblong or linear outer whorl and a larger, petal-like inner whorl with a fleshy appendage at the base. Six or more stamens are present, often with flattened filaments. The beaked oblong ovary is divided into six chambers (carpels) by strongly developed placentas, each containing many ovules, and bears six linear styles that are partially bifid.
The tapering, oblong fruits are enclosed within the floral bract and bear three to six wings; they contain numerous small, oblong seeds.
Based on floral structure, the genus has been proposed to be divided into two subgenera: subgenus Ottelia (bisexual flowers) and subgenus Boottia (unisexual flowers), each further split into two sections based on spathe flower number and carpel count.
The highest species diversity occurs in central Africa (approximately 13 species) and southeast Asia (approximately 8 species). Species are under increasing pressure from pollution of water bodies, climate change, and habitat fragmentation.
Distribution
Ottelia is distributed throughout the Paleotropics — from Africa to Asia, Australia, New Caledonia, and Brazil. The greatest species richness is found in central Africa (approximately 13 species) and southeast Asia (approximately 8 species). Plants grow primarily in lakes, slow-flowing creeks, and rivers.
Ecology
Species of Ottelia are aquatic herbs of standing or slow-moving freshwater: lakes, ponds, sluggish streams, and rivers. They are largely submerged or emergent, rooted in substrate, and occur throughout tropical and subtropical lowland water bodies across the Paleotropics.
Conservation
Species of Ottelia face growing threats from water-body pollution, climate change, and habitat loss. Rising water temperatures and changing hydrological conditions are accelerating habitat fragmentation, and the trend of decline is expected to continue as climate change intensifies.
