Eleocharis

Eleocharis is a genus in the sedge family, Cyperaceae, containing 250 or more species of flowering plants. Commonly called spikerushes or spikesedges, the genus is found nearly worldwide. Its greatest diversity occurs in the Amazon rainforest and the adjacent eastern slopes of the South American Andes, as well as in northern Australia, eastern North America, California, Southern Africa, and subtropical Asia. Almost all Eleocharis species live in aquatic or moist habitats, ranging from sea level up to over 5,000 meters in elevation in the tropical Andes.

The genus is fairly easy to identify: every Eleocharis species has photosynthetic stems but lacks green leaves—the leaves are reduced to sheaths around the stem bases. Many species are robust, spreading by rhizomes in lowland tropical wetlands.

Others are small, clump-forming annuals or perennials that grow near streams, and some fall in between. A number of species are obligate aquatics, usually with submerged, branching stems and notable photosynthetic adaptations, such as the ability to switch between C3 and C4 carbon fixation depending on environmental conditions. In all species, the flowers appear on unbranched, terminal spikelets at the tips of the stems.

Despite the genus’s diversity, the taxonomic features useful for distinguishing species are few, making many species very hard to tell apart. Several currently recognized species with broad geographic ranges are highly variable, and some likely contain multiple independent evolutionary lineages. Because of this difficulty, many botanists avoid collecting these plants, so many species are underrepresented in the botanical record.

One of the best-known species is the Chinese water chestnut, Eleocharis dulcis. It produces tubers on its rhizomes that can be peeled and eaten raw or boiled. In Australia, magpie geese depend almost entirely on these tubers for a large part of the year.