What are sedges?
Grasses, Sedges and Rushes all belong to the same plant family, that of Flowering plants (Angiosperms) and so are frequently confused with each other as they often have very similar characteristics. An old saying that often helps differentiate them – although it is not totally reliable – is: “Sedges have edges, rushes are round and grasses are hollow right up from the ground!”
Another easy way to differentiate them is that sedges generally don’t have those sweet-tasting nodes or the hollow stems that grasses have.
Sedges belong to the Cyperaceae family of plants. There are 5,500 known species of sedge and 90 subspecies (genera) worldwide. This includes the largest group, True sedges (Carex).
Sedges are what we call “Monocotyledons”, which means they have a single, embryonic first leaf that appears from a germinating seed. (See “Grass forms” for full explanation.)
Like grasses, sedges tend to form in either dense clumps or tufts. Unlike grasses, they usually have three-sided stems (although Bulrush sedge (Schoenoplectus) has cylindrical stems) and leaves – in the form of true leaves, flaps or sheaths – that are borne in threes in spiraling vertical positions up the stem.
Sedges have thick, fibrous roots or underground stems (either potato-like tubers or rhizomes), usually with short-spaced internodes.
As with grasses, the seed heads of sedges are usually produced at the end of a single erect, usually tufted stem. Numerous, almost inconspicuous flowers (florets) are arranged in either individual or groups of “spikes” at the top of the stem.
Normally sedges have triangular, solid stems, ranks of three spiralling leaves (or form of leaf) and flowers on spikes, whereas grasses have cylindrical, usually hollow stems with nodes (swollen joints), alternate leaves (appearing in pairs) and flowers.
Sedges are particularly associated with wetlands or areas of poor-quality, moist soil, particularly in tropical Asia and South America. “Sedgelands” are areas heavily populated with sedges.
Sedges have a diverse distribution and can be found in all parts of the world except Antarctica. They grow in a broad range of habitats and altitudes, from the Arctic tundra through to temperate and tropical regions and are predominant plants in many wetlands. They also like man-made habitats such as canal banks and ditches.
Most sedges are bisexual and more rigid in form than grasses and so are less adept at catching the pollen as it passes through the air.
Once pollinated, the ovary in most species of sedge forms a tiny, single-seed, nut-like fruit which is dispersed either on the wind, by flotation or by sticking to passing animals.
The most well-known sedges are the Water chestnut (Eleocharis dulcis) and Papyrus sedge (Cyperus papyrus) – from which papyrus paper was made – and Bulrushes (Schoenoplectus), Cotton-grass (Eriophorum), Spike-rush (Eleocharis), Sawgrass (Cladium), Nutsedge/Nutgrass (Cyperus rotundus) and the White-star sedge (Rhynchospora colorata). Interestingly, the inappropriately named Bulrush (Typha latifolia/Schoenoplectus lacustris) and the Club-rush (Holoschoenus vulgaris) are also sedges and not rushes.
Sedges you are most likely to come across are the Pond sedge, True sedge, Black sedge, Tawny sedge, Bog sedge, Spring sedge, Pendulous sedge, Common spike-rush, Cotton sedge, Bulrush sedge.
References: United Nations Environment Programme (UNEP), Division of Technology, Industry and Economics; Botany for gardeners, Brian Capon, Third edition, Timber Press; Colour Identi cation Guide to the Grasses, Sedges, Rushes and Ferns of the British Isles and north-western Europe, Francis Rose, Viking, The Penguin Group; Royal Botanical Gardens, Kew, London; Missouri Botanical Garden; Latin for gardeners, Lorraine Harrison, Royal Horticultural Society; International Botanical Congress (IBC); RHS Gardeners’ encyclopaedia, Christopher Brickell ed., Dorling Kindersley; The Royal Horticultural Society; The Wild Flower Key, Frances Rose, Warne; Oxford English Dictionary, Oxford University Press.