Rushes
Rushes
Rushes are monocotyledonous plants in the genus Juncus. Rushes make up most of the species in the family Juncaceae. There are about 400 species in the rush family, distributed among eight or nine genera. The most species-rich groups are the rushes (Juncus spp.) with 225 species, and the wood-rushes (Luzula spp.) with 80 species.
Species in the rush family occur worldwide, but they are particularly abundant in moist and wet habitats of cool-temperate, boreal, arctic, and alpine zones, especially in the Northern Hemisphere.
Biology of rushes
Rushes are grass and sedge like in their superficial morphology, but they differ from plants in these families (Poaceae and Cyperaceae, respectively) in important respects.
Most species of rushes are herbaceous perennial plants, although a few have an annual life cycle. Many species of rushes typically grow erect, but a few grow close to the ground surface. The stems of rushes are usually hollow, cylindrical, or somewhat flattened, and often with occasional cross-sections or nodes. The leaves of rushes are commonly arranged around the base of the flowering stems, but in some species the leaves are reduced to small sheaths around the flower-bearing shoots. The roots of rushes are generally fibrous, and some species have well developed systems of rhizomes.
Rushes have small, inconspicuous florets with many reduced floral parts. The florets are typically
aggregated into inflorescences or groups of various types and are wind-pollinated. Each floret typically contains both staminate and pistillate parts and is therefore bisexual. The fruit is a small capsule that contains large numbers of tiny seeds.
Rushes in North America
Many species of rushes are native to North America, but some of these are also found on other continents. The Baltic rush (Juncus balticus) is a very widespread species and is common along moist lake-shores in Eurasia and in North and South America. The soft rush (J. effusus) and path rush (J. tenuis) are similarly cosmopolitan species. Unlike the previous species, which are perennial, the toad rush (J. bufonius) is an annual species of moist soils, and it also has a very wide distribution, occurring on most continents.
Some species of rushes can grow as aquatic plants that root in the sediment of shallow water but grow into the atmosphere where they develop their flowers.
KEY TERMS
Cosmopolitan— In biogeography, this refers to species that are widely distributed, occurring on many of the continents, as are the cases of some species of rushes.
Floret— This is a small flower, often with some reduced or missing parts. Florets are generally arranged within a dense cluster.
Inflorescence— A grouping or arrangement of florets or flowers into a composite structure.
Rhizome— This is a modified stem that grows horizontally in the soil and from which roots and upward-growing shoots develop at the stem nodes.
Examples of these relatively tall rushes include Juncus articulatus and J. militaris which can grow as tall as 3.3 ft (1 m).
Rushes in ecosystems
The usual habitat of rushes is wetlands of many types, including marshes, fens, wet meadows, and the shallow-water edges of streams, ponds, and lakes. Rushes can be quite abundant and productive in some of these habitats, but they rarely dominate the vegetation over an extensive area.
Rushes are an important component of the habitat of many species of animals, especially in wetlands. For example, some of the best habitats for waterfowl will have an abundant component of rushes. Some species of birds eat the seeds of rushes, while other species graze on the leaves and shoots.
Economically important rushes
Rushes are not of much direct economic benefit to humans. The Japanese mat rush or soft rush (Juncus effusus) and the wicker rush (J. squarrosus) are used for weaving and making wicker chair-bottoms. Rushes are rarely cultivated for these purposes. The raw materials are usually collected from habitats that are being managed for other purposes or from natural wetlands.
Rushes are sometimes abundant in pastures, but they are not a preferred forage species because their stems are not very palatable or nutritious for domestic livestock.
Rushes also provide useful ecological functions in some of the habitats in which they are abundant. For example, on sloping ground with moist soil rushes may be important in binding the surface soil and thereby helping to prevent some erosion.
A few species of rushes have naturally spread or been introduced by humans beyond their native habitats and are considered to be weeds in some parts of their new range. In North America, the soft rush and path rush (J. tenuis) are minor weeds of pastures, lawns, and some other habitats.
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