Ottelia

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Ottelia is a genus of aquatic plants in the Hydrocharitaceae family. Described as a genus in 1805, it is native to tropical and subtropical regions of Africa, Asia, South America, Australia, New Caledonia, and Brazil. The plants are very variable in form but all live in water. They usually have crowded leaves; some leaves stand on short stems, others float on long stems, and the rooting stem is long.

Flowers grow inside a leaf-like bract and have a tubular spathe that splits into two. Each flower has two rings of a six-part perianth above the ovary. The outer part is rigid and oblong or linear, while the inner part is petal-like with a fleshy base. There are six or more stamens, often with flattened filaments. The ovary is oblong and beaked, with placentas that divide it into six chambers containing many ovules. There are six linear styles that partly split. The fruit is oblong, enclosed in the floral bract, with three to six wings and contains many small, oblong seeds.

There are ideas to divide Ottelia into two subgenera and four sections. It is the second largest genus in its family and is found across the Paleotropics—from Africa to Asia to Australia, including New Caledonia and Brazil—with the most species in central Africa (about 13) and Southeast Asia (about 8). They typically grow in lakes and slow-moving creeks and rivers.

Originating in the mid Miocene, Ottelia now has two major lineages corresponding to Africa and Asia. It likely began in Africa and spread by ocean currents to South America and Australia, then from Australia to Asia. Climate changes, the East Asian monsoon, and tectonic movements helped diversification, especially in China, where the uplift of the Yunnan-Guizhou Plateau may explain high endemism.

Ottelia is the second largest genus in its family, but many species are increasingly threatened by water pollution, climate change, habitat loss, and warming water temperatures.