Cyperaceae

Lore & Background

Sedges are distinguished from grasses and rushes by stems with triangular cross-sections (with occasional exceptions, such as tule, which has a round cross-section) and leaves that are spirally arranged in three ranks. This contrasts with grasses, which have alternate leaves in two ranks, leading to the mnemonic 'sedges have edges' to differentiate them from generally round rushes or hollow, noded grasses. Some well-known sedges include the water chestnut (Eleocharis dulcis) and the papyrus sedge (Cyperus papyrus), from which the writing material papyrus was made. Other members include cotton-grass (Eriophorum), spike-rush (Eleocharis), sawgrass (Cladium), nutsedge or nutgrass (Cyperus esculentus/Cyperus rotundus, both a cultivated crop and common weed), white star sedge (Rhynchospora colorata), and umbrella sedge (Cyperus alternifolius).

Reader's Guide

Members of the Cyperaceae family are characterized by the formation of dauciform (carrot-like) roots, an alteration in root morphology that researchers regard as analogous to cluster roots in Proteaceae, which help uptake nutrients such as phosphorus from poor soil. Like other members of the order Poales, sedges are mostly wind-pollinated, but there are exceptions: Cyperus niveus and Cyperus sphaerocephalus have more conspicuous flowers and are insect-pollinated. Researchers have identified prominent sedges occurring at least as early as the Eocene epoch, with earlier fossils dating to the Late Cretaceous. The family's ecological significance lies in its dominance of sedgelands and sedge meadows, particularly in wetlands and poor soils, where they play a key role in nutrient cycling and habitat structure.

Did You Know?

• Sedges have stems with triangular cross-sections, leading to the mnemonic 'sedges have edges' to distinguish them from round rushes or hollow grasses.
• The papyrus sedge (Cyperus papyrus) was used to make the writing material papyrus.
• Some sedges, such as Cyperus niveus and Cyperus sphaerocephalus, are insect-pollinated, unlike most sedges which are wind-pollinated.
• Fossil evidence of sedges dates to the Late Cretaceous, with prominent sedges occurring at least as early as the Eocene epoch.