Sedges
Sedges
Sedges are monocotyledonous plants in the genus Carex that make up most of the species in the family Cyperaceae. This family consists of about 4,000 species distributed among about 90 genera, occurring world-wide in moist habitats in all of the major climatic zones. The sedges are the largest group in the family with about 1,100 species, followed by the papyrus or nut-sedges (Cyperus spp.; 600 species), bulrushes (Scirpus spp.; 250 species), and beak-rushes (Rhynchospora spp.; 250 species).
The major importance of sedges and other members of this family is their prominent role in many
types of ecological communities and the fact that they are an important source of food for many species of grazing animals. A few species are also of minor economic importance as food for humans.
Biology of sedges
Sedges are superficially grass like in their morphology, but they differ from the grasses (family Poaceae) in some important respects.
Most species of sedges are perennial plants, with only a few having an annual life cycle. Sedges are herbaceous, dying back to the ground surface at the end of the growing season but then re-growing the next season by sprouting from underground rhizomes or roots. One distinguishing characteristic of the sedge is its three-angled or triangular cross-section of the stem.
The flowers of sedges are small and have some reduced or missing parts. Referred to as florets, they are either male (staminate) or female (pistillate), although both sexes can be present in the same cluster of florets, or inflorescence. Usually, the staminate florets occur in a discrete zone at the top of the inflorescence, with the pistillate florets beneath. Sedges achieve pollination by shedding their pollen to the wind, which then carries these grains to the stigmatic surfaces of female florets. The fruits of sedges are dry, one-seeded achenes, sometimes enclosed within an inflated structure called a perigynium.
Wetlands are usually the habitat for various types of sedges. Sedges may occur as terrestrial plants rooted in moist ground or as emergent aquatic plants, often rooted in the sediment of shallow water at the edge of a pond or lake, but with the flowering stalk and some of their leaves emergent into the atmosphere. Some species of sedge can occur in habitats that are rather dry, as in the case of some arctic and alpine sedges.
Sedges in ecosystems
Sedges are an important component of the plant communities of many types of natural habitats, particularly in marshes, swamps, and the shallow-water habitats along the edges of streams, ponds, and lakes. Because sedges are a relatively nutritious food for grazing animals, places rich in these plants are an important type of habitat for many types of herbivorous animals. These can range from the multitudinous species of insects and other invertebrates that feed on sedges, to much larger grazing animals such as elk (Cervus canadensis ), white-tailed deer (Odocoileus virginianus ) and other herbivores. Even grizzly bears (Ursus arctos ) will feed intensively on sedges at certain times of the year when other sources of nutrition are not abundant, for example, in the springtime after the bear has emerged from its winter hibernation.
Sedges and their relatives can sometimes dominate extensive tracts of vegetation, especially in places where shallow-water wetlands have developed on relatively flat terrain. For example, the extensive marshes and wet prairies of the Everglades of south Florida are dominated by the sawgrass (Cladium jamaicensis ), a member of the sedge family.
Economically important sedges
No species of true sedges (that is, species of Carex) are currently of direct economic importance to humans. However, a few species in other genera of the sedge family are worth mentioning in this respect.
KEY TERMS
Achene —A dry, indehiscent, one-seeded fruit, with the outer layer fused to the seed.
Floret —A small flower, often with some reduced or missing parts. Florets are often arranged within dense clusters, such as the inflorescences of species in the sedge family.
Inflorescence —A grouping or arrangement of florets or flowers into a composite structure.
Perigynium —A sac-like bract that surrounds the ovary or seed in many members of the sedge family.
The papyrus or paper rush (Cyperus papyrus ) grows abundantly in marshes in parts of northern Africa and elsewhere, where it has been used for millennia to make paper, to construct reed-boats, to make thatched roofs, to strengthen dried mud-bricks, and for other purposes. There are numerous biblical references to the great abundance of papyrus that used to occur in wetlands in northern Egypt, but these marshy habitats have now been drained, and the species is considered to be rare in that region.
The stems of papyrus and other species of Cyperus and the related bulrushes (Scirpus spp.) have also been used for weaving into mats and baskets. The Chinese mat grass (Cyperus tegetiformis ), which is commonly used for matting in eastern Asia is an prime example of these related bulrushes.
The bulbous tubers of the edible nut-sedge (Cyperus esculentus ) and the water chestnut (Eleocharis tuberosa ) are harvested and eaten as a starchy food. The water chestnut probably originated in China and the edible nut-sedge in Egypt.
A few species of sedges and related plants are considered to be significant weeds in some places. In North America, for example, the edible nut-sedge has escaped from cultivation and has become a weed of wetlands in some regions.
Resources
BOOKS
Judd, Walter S., Christopher Campbell, Elizabeth A. Kellogg, Michael J. Donoghue, and Peter Stevens. Plant Systematics: A Phylogenetic Approach. 2nd ed. with CD-ROM. Suderland, MD: Sinauer, 2002.
Bill Freedman