Word of the Week: Sedge

sedge [sej] noun: a wetland plant of the Cyperaceae family that resembles grass, but differs in having achenes, solid, often triangular stems, linear leaves and monocotyledonous spikelet inflorescences

Many gardeners were taught the short rhyme, “Sedges have edges, rushes are round, and grasses are hollow, straight to the ground,” as a short-hand way of distinguishing between the three somewhat similar plant types. Some versions of the rhyme say “grasses have knees that bend to the ground”–meaning they have jointed stems. The stems of sedge plants, on the other hand, are not hollow, but filled with pith, a spongy tissue. They are mostly triangular, hence the edges, though there are exceptions, a good reminder that in the biological sciences, almost nothing, no rule or law or identifying sign, is always true.

The Cyperaceae are the third largest monocot plant family, with 5,000 species and 104 genera, of which by far the largest genus is Carex, which accounts for over 2,000 of those species. Though traditionally seen as closely related to the Poaceae (grasses), recent research indicates the sedges are more closely related to Juncaceae (rushes).

Sedge leaves usually are parallel veined with a basal sheath closed around the stem and 3-ranked (each leaf emerges one-third of the way around the stem from the leaf below). Gardeners should keep in mind the point about the edges when working with sedges. Some leaves are saw-toothed; many are capable of inflicting paper-cut-like damage to hands trying to pull them – it is wise to wear gloves. Some sedges attract butterflies that use the leaves as hosts for their caterpillars.

Many sedges produce spikelets where the blooms and fruits appear. Their inconspicuous flowers can be perfect (with male and female parts together) or imperfect with separate staminate (male) and pistillate (female) spikelets. Most sedges are wind-pollinated, not relying on insects for pollination.

Whereas grasses produce grains and rushes capsules, sedges produce achenes. A Carex achene is encased in a perigynium subtended by a bract, both of which are diagnostic and aid in species identification. The achenes of some water sedges are consumed by waterfowl. Though a few sedges are annuals, most are perennials that spread by rhizomes, stolons, corms, or tubers. The tubers of some sedges are starchy or nutty and can be used as food for humans (such as Cyperus esculentus L., var sativus, known as chufa, cultivated for over 6000 years) as well as for wildlife.

Cyperus papyrus (papyrus) at Kew Gardens, London, England.
Photo courtesy of Adrian Pingstone

Sedge is an old word, first appearing in its current use in the English language around 1200, according to Merriam Webster. However, the plant Cyperus papyrus was known well before that. The ancient Egyptians used it 4500 years ago to make a substance they wrote on. Our English word paper comes from that Latin plant name, and papyrus plants are still cultivated as ornamentals used in water gardens.

Important to wetland ecosystems, sedges control erosion and filtrate water. On the negative side, sedges are also regarded as some of the worst agricultural weeds in the world. Hitting number 1 on the list for many is Cyperus rotundus (purple nutsedge), an aggressive perennial, which not only spreads fast but is hard to eradicate. Like Cyperus esculentus (yellow nutsedge), another noxious agricultural weed, it is allelopathic and the chemicals they both produce suppress crop yields, especially in heavily infested fields. (For weed identification and control, refer to Virginia Cooperative Extension’s Common Turf Weeds.)

Reference

Carter, RC. An Introduction to Sedges, Herbarium, Biology Department, Valdosta State University, Valdosta, GA 31698. https://mypages.valdosta.edu/rcarter/2006.Tallahassee.Native%20Plants.01.pdf.

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