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U.S. Forest Service

Plant of the Week

USDA Plants distribution map for the species. Carex cumulata range map. USDA PLANTS Database.

Carex cumulata. Clustered sedge habitat on Rattlesnake Mountain in Rumney, New Hampshire, on White Mountain National Forest. Photo credit: New England Wild Flower Society.

Carex cumulata. Close-up of fruiting structure (note the very round nature of each spikelet). Photo credit: New York Natural Heritage Program.

Carex cumulata. Clustered sedge habit. Photo credit: Ben Kimball, New Hampshire Natural Heritage Program.

Clustered Sedge (Carex cumulata (L. H. Bailey) Fernald)

By Alice Schori

Clustered sedge is a member of the Cyperaceae or sedge family, grass-like plants that often have triangular stems (“sedges have edges”). It lives up to its name in two senses: it grows in dense clumps, and its fruits (perigynia) appear in a group of tight clusters at the summit of a stiff, usually upright stem (culm). The name in French also reflects this: “carex dense.” In some states it is known as “piled-up sedge”, and a Latin synonym is Carex straminea Willdenow ex Schkuhr var. cumulata L. H. Bailey.

Although sedges are often tricky to identify, this one is rather distinctive. The stiffly upright habit of this plant with rosettes of 3 to 6 millimeters wide, yellow-green basal leaves is unusual and eye-catching. Fruiting culms can range from 20 to 80 centimeters tall, and many culms may emerge from one clump. On each fertile culm, there are usually 2 to 4 small leaves. Sheaths, where the leaf blade is attached to the culm, are green-veined nearly to the collar (upper edge) on the side of the stem opposite the blade, with a white-translucent band or Y-shaped region at the collar. The seed-head or inflorescence consists of 3 to 10 conic to ovoid spikes, with truncate or rounded bases and obtuse tips, often fairly closely spaced but sometimes with small gaps between them. They are light green in color, but eventually turn brown. Perigynia are tightly oppressed, obovate (almost round, but widest above the middle), flat and winged, with flat beaks that are brown at the tip and have finely toothed edges.

Clustered sedge plants are perennial and fruit in July to August. They occur mostly in dry habitats but can sometimes be found in drying peat bogs. More commonly, they are found in acidic sandy, gravelly, or rocky soils of barrens, acidic woods, and thickets. Clustered sedge is usually infrequent and seldom abundant in the habitats in which it is occurs. It is listed as endangered in Connecticut, Indiana, and New Jersey; threatened in New Hampshire; and special concern in Rhode Island and Wisconsin.

If you want to find this sedge, try visiting its favored habitat a year or two after a fire. In the White Mountain National Forest, it persists in small numbers in openings around rocky outcrops or ledges on mostly south-facing slopes dominated by oak and pine, but in recent decades, fires on Rattlesnake Mountain have led to amazing population explosions of Carex cumulata the year following a fire, with numbers tapering off gradually over the next ten years or so as brushy vegetation grows back in and shades it out.

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