Spikerushes
Eleocharis – also known as spikerushes – can be found in the Amazon, close to the slopes of the South American Andes, Northern Australia, eastern North America, California, Southern Africa, and Asia. They usually live in water that is sea level or more than 5,000 meters in elevation.
The genus itself is relatively easy to recognize; all Eleocharis species have photosynthetic stems and lack leaves (the leaves have been reduced to sheaths surrounding the base of the stems). Many species are robust and spread plants of lowland tropical wetlands, while many others are small annual or perennial herbs growing near streams, and still others are intermediate.
There are also a number of species that are obligate aquatic species, which usually have submerged, branching stems and often exhibit interesting photosynthetic adaptations, such as the ability to switch between C3 and C4 types of photosynthesis in response to different environmental stimuli. In all 250 Eleocharis species, the flowers are borne on unbranched terminal spikelets at the apices of stems.
In spite of the diversity of the genus itself, taxonomic characters useful for delimiting species within it are few and many species are very difficult to tell apart. Many currently recognized species with very wide geographic ranges are highly polymorphic. Some of these species probably contain multiple independently-evolving lineages. Because of their difficult nature, many botanists avoid collecting these plants and so many species are under-represented in the botanical record.
One of the best known species is the Chinese water chestnut, Eleocharis dulcis. These plants bear tubers on their rhizomes which may be peeled and eaten raw or boiled. In Australia, magpie geese rely almost exclusively on these tubers for sustenance for a significant portion of the year.