Carex comosa Boott

Cyperaceae (Sedge Family)

07/10/00

Bristly sedge is one of our most common sedges.  It’s found in very shallow water where there’s little water level fluctuation. It’s a long-lived plant that grows in erect clumps at the edges of ponds and bogs and in shallow marshes, where the pH is near neutral to slightly acid.  It tolerates some shade and it spreads slowly by seed and by rhizomes, with new shoots that sprout in fall and overwinter.

Sedges are grass-like plants with inconspicuous flowers, but it’s easy to distinguish sedges from grasses based on a few vegetative characters. The base of many sedges, especially the genus Carex, is triangular and solid in cross section.  Grass stems are round or flattened in section and hollow between with the nodes. Sedges include the Egyptian papyrus and the the “sawgrass” of the Everglades.

The leaves of many sedges are folded into an “M” in cross section, as in the lower left of the photo.  Each flower has a single scale and, in the genus Carex, the seed or nutlet is enclosed in a papery sac or “perigynia”. These perigynia are clustered in spikelets. Wisconsin has over 150 species of Carex that grow in a variety of wetland and upland habitats.  The arrangement of the spikelets and mature perigynia are usually needed for positive identification to species.

The genus Carex is divided into two large groups. C. comosa is part of the “bladder sedge” group. Perigynia in this group are  inflated with an air space between the perigynia wall and the seed. They also have long spikelets, each either entirely male or entirely female, and long leafy bracts below the spikelets.

C. comosa has a single male spikelet on top (tan in the photo) above 4 to 5 female spikelets (4 in the photo).  The green female spikelets are up to 7 cm long and 1 cm wide and at least the bottom female spikelet hangs downward on a slender stalk.  Each perigynia ends in two divergent curved teeth at least 1 mm long. These create the bristly appearance of the female spikelet that gives the sedge its common name.

Other carices with similar spikelet arrangement, C. pseudocyperus and C. hystericina, have straight, rather than divergent, teeth on the perigynia, so the spikelets appear less bristly. C. hystericina is also smaller overall, with a tinge of red at the base of the leaves, and only 2 to 3 female spikelets.