Carex sterilis (Sterile Sedge)

Plant Info
Also known as: Dioecious Sedge
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Status:
  • State Threatened
Habitat:sun; wet; calcareous fens
Fruiting season:June - July
Plant height:6 to 30 inches
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Spikes: Flower shape: indistinct Cluster type: spike

[photo of male and female spike clusters] A cluster to 1½ inches long at the top of the stem, made up of 3 to 8 spikes (usually 4 or 5). Plants commonly have staminate (male) and pistillate (female) spikes on separate plants; all-staminate spikes crowded at the stem tip and all-pistillate spikes more loosely arranged. Bracts at the base of spikes are inconspicuous or absent altogether.

[photo of mixed male and female spikes] Sometimes, a stem will have all staminate spikes at the tip and 1 or more all-pistillate spikes below it, or the lowest staminate spike with just a few pistillate flowers, or a few staminate flowers on an otherwise all-pistillate stem. Occasionally the spikes are mixed up with a more random arrangement of staminate and pistillate flowers.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath and ligule] Leaves are alternate with 3 to 5 leaves on the lower fourth of the stem, up to 10 inches long, 1.2 to 2.6 mm wide, flat or pleated, hairless, rough along the edges especially near the tip. Some leaves may initially rise above some flowering stems but most do not. Stem leaf sheaths tightly wrap the stem and are translucent whitish, concave at the tip. The ligule (membrane where the leaf joins the sheath) is wider than long and rounded at the tip. A few old, dead leaves may persist to the next season.

[photo of plant base] Bases are wrapped in a brown sheath that is not fibrous. Stems are erect to ascending, slender, 3-sided, rough textured on the upper stem, and may elongate up to about 30 inches at maturity. Plants are densely clump-forming from a mix of flowering and vegetative stems.

Fruit: Fruit type: seed_without_plume

[close-up of maturing spikes] Fruit develops in late spring through early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Pistillate spikes each contain 3 to 26 fruits that are mostly spreading to reflexed (downward pointing).

[photo of perigynia, scale and achene] Pistillate scales are egg-shaped to oblong, translucent white to brown-tinged with a green midrib, pointed at the tip, awnless, about ¾ as long as the perigynia. Perigynia are 2.1 to 3.8 mm long, 1.2 to 2.2 mm wide, green turning golden to dark chestnut brown at maturity, hairless, thickened and spongy at the base, flattened on the back side, finely 5 to 12-veined on the front, veinless or sometimes veined on the back, teardrop to egg-shaped to nearly triangular in outline and widest at the base, tapering at the tip to a beak .4 to .8 mm long that is at least half as long as the body and is minutely toothed along the edges. Achenes are 1 to 1.7 mm long, .9 to 1.3 mm wide, flattened lens-shaped, about as long as wide, broadest near the base, and mature to golden yellow.

Notes:

Carex sterilis is a rare sedge of calcareous fens, a protected type of wetland, mostly in the prairie regions of the state with a few populations in the northern patterned peatlands, areas known as “spring fens”. According to the DNR, while there are numerous populations of C. sterilis in Minnesota, the calcareous fens it habitats are small, scattered, and threatened by incompatible land uses that alter the hydrology of these fragile systems, sometimes from miles away. C. sterilis was listed as a Threatened species in 1984.

Carex is a large genus, with over 600 species in North America and 150+ in Minnesota alone. They are grouped into sections, the species in each group having common traits. Carex sterilis is a member of the Stellulatae section; some of the section's common traits are: clump forming, basal sheaths not fibrous, leaves V-shaped in cross-section when young, usually 2 to 10 spikes per stem, terminal spike staminate or pistillate or with pistillate flowers at the tip (gynecandrous), pistillate scales blunt to pointed at the tip, perigynia widely spreading, hairless, veined at least on one side, spongy at the base, 2 short teeth on the beak, achenes lens-shaped. There are similarities with some members of the Phaestoglochin section, which have spikes with staminate flowers above the pistillate (androgynous).

Carex sterilis may be distinguished from other Carex species by: 3 to 8 (commonly 4 or 5) spikes at the tip of the stem, usually some plants all-staminate, some all-pistillate, frequently with at least a few in a population that are mixed; perigynia 2.1 to 3.8 mm long, spongy at the base, egg-shaped to nearly triangular in outline and widest at the base, veined on one side, sometimes both sides, tapering to a beak at least half as long as the body; achenes lens-shaped, about as long as wide and widest near the base.

Carex sterilis is most likely to be confused with Carex interior, with which it may grow. C. interior commonly has 3 gynecandrous spikes each with up to 15 perigynia, the terminal spike with a well-developed staminate portion below the pistillate flowers, perigynia are usually less than 3 mm long with a shorter, more abruptly tapered beak less than half as long as the body. Somewhat similar is Carex echinata, which is more like C. interior but more commonly has 4 to 6 spikes, perigynia up to 3.6 mm long with a more gradual taper to a longer beak. As with most Carex, several plants in a population should be checked for these traits.

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More photos

Photos by K. Chayka taken in Mahnomen County. Photos by Peter M. Dziuk taken in Mahnomen, Marshall and Pope counties. Photos by Steve Eggers taken in Scott County. Other photos courtesy John Thayer.

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