Sedges differ from grasses by having a 3-angled stem and structurally different flowers where the female flowers are enclosed in a sac like structure called the perigynium, which is subtended by a single scale. Lake Sedge is a perennial colonial sedge, one of the largest sedges, growing 6 to 50 inches high, on stout unbranched stems (culms) with smooth surfaces except the upper areas may be rough to the touch. Plants usually produce leafy sterile stems that are numerous and shorter. Fertile stems are frequently arching over when in fruit.
The basal leaf sheaths are reddish purple, blade-less, and on the front strongly with a lattice of feather-like fibers (fibrillose). Ligules of leaf blades are less than 30 to 40 mm long, much longer than wide. Upper blade sheaths are smooth.
The leaf blades are 8.5 to 21 mm wide, a flattened M shape, coarse, without hair, pale green to grayish blue in color, sometimes with a whitish bloom on the underside. The longest blades will exceed one meter. Lower parts of the stems are leafy.
The inflorescence at the top of the stem has multiple spikes, 17 to 60 cm in total length. There are 2 to 4 spikes lateral spikes on the lower section of the inflorescence that are pistillate, ascending to arching, stalkless or with short stalks. Each pistillate spike can be 2 to 10 cm long, and thick - 10 to 15 mm wide. The terminal and upper spikes are staminate. These are erect and number 3 to 5 usually, 1 to 8 cm long and very narrow, only 3 to 4 mm wide, stalkless except for the terminal spike. These are short-lived. Each pistillate spike has perigynia that are narrowly ovoid to narrowly ellipsoid, ascending and densely packed on the spike. (The bladder-like sacs that enclose the female flower and later the fruit are called perigynia, singular - perigynium). The bracts that form at the base of the lower spikes are leaf-like, shorter than the length of the inflorescence. These are usually without sheaths.
Each perigynium is strongly 14-28 veined, smooth surfaced with the body gradually tapering to an obscure beak 0.5 to 1.6 mm long with a pair of pointed straight teeth. The body of the perigynium is olive-green, thick-walled, and roughly 5.2 to 7.8 mm long and 1.6 to 2.5 mm wide. The scales of the pistillate perigynia are half the length of the perigynium, smooth, lanceolate to ovate in shape, translucent with a green mid-vein initially then turning purplish-brown to black in color, with a small, 0.3 to 3.5 mm awn. There are three stigmas per pistillate floret.
Seed: Mature fruit is a brown ellipsoid achene, (basically 3-angled) with a persistent style. Each is about 2.0 to 2.6 mm long and usually is retained inside the perigynium when the perigynium detaches from the spike. Florets are wind pollinated.
Habitat: Lake Sedge grows from creeping rhizomes, forming colonies in wet to wet-mesic conditions such as in marshes, alder thickets, wet and open thickets, sedge meadows, fens, and riparian shores. Plants prefer full sun but will grow in partial sun to shade.
Names: The genus name, Carex, is from the Latin, being the old name for Sedges. The species, lacustris, is appropriate as it means 'pertaining to lakes', referring to the type of habitat this sedge prefers. The author name for the plant classification - ‘Willd.’ refers to Carl Ludwig Willdenow (1765-1812), German botanist, a founder of the study of the geographic distribution of plants. He was director and curator of the Botanic Garden of Berlin. The alternate common name of 'Hairy Sedge', while used by some major reference sources, is somewhat misleading as there is very little hair on this species.
Comparisons: Lake Sedge is a member of the sedges in the Section Paludosae, and has the distinguishing characteristics of wide M-shaped leaf blades, ladder-fibrillose basal sheaths, raceme type inflorescences with multiple spikes, upper spikes staminate and lower spikes pistillate. 3 stigmas per floret. The most similar sedge like this is C. hyalinolepis, the Ditch Sedge, where the longest ligules are less than 2x longer than wide and the perigynia are obscurely 10-15 veined. However, C. hyalinolepis is not found in Minnesota. The sedge in our area that is most confusing, while not in this sedge section, is C. atherodes, the Slough Sedge which is found in similar habitats to Lake Sedge. There the noticeable differences are leaf blades only 3 to 10 mm wide, sterile stems longer than the fertile stems, the perigynia larger (7 to 12 mm by 1.8 to 3.8 mm), only 12 to 21 veined, the the teeth of the beak spreading to out-curved. It is found in many of the same counties of Minnesota as C. lacustris.
Above: The staminate spikes. Drawing courtesy Kurt Stüber's Online Library.
Below: The inflorescence. 1st photo - at flowering time. 2nd photo - post flowering.
Below: Pistillate spike nearing maturity. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 3 stages of the staminate spikes - before flowering, at flowering and past flowering.
Below: Detail of a maturing pistillate spike.
Below: Mature perigynia.
Below: Front and back views of the sheath area.
Below: The stem base and leaf blade detail - note the 3 prominent ridge lines creating the "M" shape.
Lake Sedge is one of over 150 sedges native to Minnesota. It is widespread in the state but the cluster of those counties not reporting it are in the drier SW and the farm counties of southern Minnesota where much wetland drainage has occurred. In North America it is found from the Great Plains eastward in the U.S. but not in the southern tier of states, and in Canada from Alberta eastward in the lower provinces.
At Eloise Butler it has been noted in the Garden on both the 1986 and 2009 Garden Plant Census.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"