sterile sedge

(Carex sterilis)

Conservation Status
sterile sedge
 
  IUCN Red List

not listed

     
  NatureServe

NNR - Unranked

S2 - Imperiled

     
  Minnesota

Threatened

     
           
Wetland Indicator Status
     
  Great Plains

OBL - Obligate wetland

     
  Midwest

OBL - Obligate wetland

     
  Northcentral & Northeast

OBL - Obligate wetland

     
           
 
Description
 
 

Sterile sedge is a stiffly erect, 4 to 29 tall, perennial sedge rising from a very short underground stem (rhizome). It usually forms dense clumps. It is often the dominant species.

Sterile stems are poorly developed and are mostly reduced to basal clusters of leaves. Basal leaves are reduced to nearly bladeless sheaths.

The flowering stem (culm) is sharply three-angled, stiff, hairless, brown at the base, and 4 to 29 long, longer than the leaves. It is not winged. The angles are rough to the touch on the upper portion of the stem. Three to five slender stem leaves, arranged in three vertical rows (ranks), appear on the lower third of the culm.

The stem leaves are green, hairless, 3 to 10 long, and 1 32to wide. The leaf blade has a single prominent midvein and is folded like a fan, at least near the base. The margins are rough to the touch. The lower part of each leaf that surrounds the stem (sheath) is thin, papery, and white or nearly white. It is not fibrous. The tip of the sheath is usually concave, sometimes straight across. The lowermost part is brown. The membrane where the leaf meets the stem (ligule) is rounded to broadly angled and 1 64 to 1 16 long. It is mostly fused to the inner face of the leaf blade but it has a loose margin.

The inflorescence consists of 3 to 8, usually 4, unisexual elongated flower clusters (spikes) at the end of the stem. The spikes are stalkless and are readily distinguished from each other. The upper spikes are crowded together but at least one spike, the lowest, is separate and does not overlap the adjacent spike. The modified leaf (bract) that usually subtends a sedge spike, is missing or inconspicuous and scale-like.

The inflorescences are highly variable. The terminal spike is usually all male (staminate) or all female (pistillate). Some plants have all staminate spikes, sometimes with a few pistillate flowers scattered on some spikes. Some plants have all pistillate spikes, rarely with a few staminate flowers scattered on some spikes. Occasionally, entirely pistillate spikes and entirely staminate spikes will be mixed on the same plant. The common name refers to the fact that some clumps are all staminate, and do not produce seed—hence, sterile.

Staminate spikes are slender, club-shaped, to 9 16 long and 1 32 to wide. They consist of 6 to 31 flowers in a dense, spiral arrangement. Each staminate flower is subtended by a single egg-shaped, 1 16 to long scale. The scale is brown with a green midrib and pale margins. The flower consists of 3 stamens with conspicuous, bright yellow, 1 32 to 1 16 long anthers. The anthers fall off soon after pollination leaving just the filaments.

Pistillate spikes are much broader, star-like, to ½ long and 3 16 to ¼ wide. They consist of 5 to 26 flowers. Each pistillate flower is entirely enclosed by a sac-like bract (perigynium) and subtended by a single scale. The scale is egg-shaped, 1 16 to long, and brown, with a green midrib and pale margins. It is narrowly pointed and is as long or nearly as long as the perigynium. The perigynium is chestnut brown to blackish, egg-shaped to almost triangular, 1 16 to long, and 1 32 to 1 16wide. It is thickened and spongy at the base and evenly tapered from the body to the tip, not forming a shoulder. It is not winged. The extended tip (beak) is 1 64 to 1 16long, a third or more of the total length of the perigynium. It is densely and irregularly toothed along the margins. Two white stigmas emerge from a small opening at the tip of the perigynium.

The fruit is a dry, yellowish-brown, egg-shaped to almost circular in outline, one-seeded capsule (achene). It is 1 32 to 1 16long, much smaller than the perigynium. It matures in June or July and drops from the plant soon after.

 
     
 

Height

 
 

4 to 29

 
     
 

Similar Species

 
  Interior sedge (Carex interior) leaves are narrower, no more than 1 16wide. There are usually only 3 spikes per stem. The terminal spike has a narrow, club-shaped, staminate portion at the base that is as long as the broad, star-like, pistillate portion above. The beak of the perigynium is no more than one fourth the total length of the perigynium.  
     
 
Habitat
 
 

Calcareous fens, calcareous wet prairies, and spring fens

 
     
 
Biology
 
 

Maturing

 
 

Mid-May to early August

 
     
 
Use
 
 

 

 
     
 
Distribution
 
 

Distribution Map

 

Sources

2, 3, 4, 5, 6, 7, 28.

 
  4/25/2015      
         
 

Nativity

 
 

Native

 
         
 

Occurrence

 
 

Widespread statewide and locally common but rare due to limited habitat

 
         
 
Taxonomy
 
  Kingdom Plantae (green algae and land plants)  
  Subkingdom Viridiplantae (green plants)  
  Infrakingdom Streptophyta (land plants and green algae)  
  Superdivision Embryophyta (land plants)  
  Division Tracheophyta (vascular plants)  
  Subdivision Spermatophytina (seed plants)  
  Class Liliopsida (monocots)  
 

Order

Poales (grasses, sedges, cattails, and allies)  
 

Family

Cyperaceae (sedge)  
  Subfamily Cyperoideae  
  Tribe Cariceae  
 

Genus

Carex (true sedges)  
  Subgenus Vignea  
  Section Stellulatae  
       
 

Synonyms

 
 

Carex elachycarpa

Carex muricata var. sterilis

Carex X minganinsularum

Kobresia elachycarpa

 
       
 

Common Names

 
 

Aroostook sedge

dioecious sedge

fan star sedge

sterile sedge

 
     
 

Unlike most plants in the genus Carex, this plant bears male and female flowers on separate plants. This characteristic gives the plant one of its common names, dioecious sedge.

 
       

 

 

 

 

 

 

 

 

Glossary

Achene

A dry, one-chambered, single-seeded seed capsule, formed from a single carpel, with the seed attached to the membranous outer layer (wall) only by the seed stalk; the wall, formed entirely from the wall of the superior ovary, does not split open at maturity, but relies on decay or predation to release the contents.

 

Beak

A comparatively short and stout, narrow or prolonged tip on a thickened organ, as on some fruits and seeds.

 

Bract

Modified leaf at the base of a flower stalk, flower cluster, or inflorescence.

 

Calcareous

Alkaline; rich in limestone; containing a high proportion of calcium carbonate.

 

Culm

The hollow or pithy stem of a grass, sedge, or rush.

 

Dioecious

Having imperfect flowers: the staminate flowers (male) and pistillate flowers (female) are borne on separate plants.

 

Ligule

In grasses and sedges, a membranous appendage at the junction of the leaf and the leaf sheath, sometimes no more than a fringe of hairs. In flowering plants, the flat, strap-shaped, petal-like portion of the corolla of a ray floret.

 

Perigynium

In Carex and other closely related sedges, a sac-like structure that surrounds the pistillate flower and later encloses the achene. Plural: perigynia.

 

Pistillate

Referring to a flower that has a female reproductive organ (pistil) but does not have male reproductive organs (stamens).

 

Rhizome

A horizontal, usually underground stem. It serves as a reproductive structure, producing roots below and shoots above at the nodes.

 

Scale

On plants, a small, usually flat and thin, modified leaf resembling the scale of a fish. In sedges, a dry, reduced bract at the base of the perianth. On animals, a small rigid plate growing out of an animal’s skin to provide protection. On butterflies and moths, a plate on the surface of the wing providing coloration.

 

Sheath

The lower part of the leaf that surrounds the stem.

 

Spike

The arrangement of an unbranched, elongated inflorescence with stalkless flowers that mature from the base toward the tip. In Cyperaceae, it also denotes a collection of one or more stalkless flowers, each subtended by scales, on a single inflorescence axis.

 

Staminate

Referring to a flower that has a male reproductive organs (stamens) but does not have a female reproductive organ (pistil).

 

Stigma

In plants, the portion of the female part of the flower that is receptive to pollen. In Odonata and Hymenoptera, a blood-filled blister or dark spot at the leading edge of each wing toward the tip, thought to dampen wing vibrations and signal mates. In Lepidoptera, an area of specialized scent scales on the forewing of some skippers, hairstreaks, and moths.

       
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