Carex molesta (Troublesome Sedge)

Plant Info
Also known as:
Family:Cyperaceae (Sedge)
Life cycle:perennial
Habitat:part shade, sun; moist to dry; prairies, woodland edges, wet meadows, wooded slopes, floodplain forest, rock outcrops, river banks
Fruiting season:June - August
Plant height:12 to 40 inches
Wetland Indicator Status:GP: FACW MW: FAC NCNE: FAC
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 spike clusters] 2 to 5 spikes (rarely 6) each 6 to 9 mm (to ~1/3 inch) long, all at the tip of the stem, overlapping and usually crowded, the inflorescence (group of spikes) erect and usually less than 1 inch long. All spikes are stalkless, erect to ascending, rounded at the tip, rounded at the base, round to oval in outline, with staminate (male) flowers at the base and pistillate (female) flowers at the tip (gynecandrous). Staminate flowers are few so spikes are more globular than club-shaped; the terminal spike may have a few more staminate flowers than lateral spikes. At the base of the lowest spike is a scale-like bract with a bristle-like tip that may be longer than the spike but does not usually overtop the terminal spike.

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

[photo of sheath and ligule] Leaves are alternate with 3 to 7 leaves on the lower third of the stem, 1.5 to 3.8 mm wide, shorter than the flowering stem, flat, hairless, rough along the edges especially near the tip. Stem leaf sheaths tightly wrap the stem and are mostly green nearly to the tip, the whitish translucent tip extends above the leaf base and is U- to V-shaped across the top edge. The ligule (membrane where the leaf joins the sheath) is about as wide as or wider than long.

[photo of plant base] Bases are wrapped in a brown sheath that may be somewhat fibrous, with old leaves often persisting to the next season. Stems are hairless, mostly erect, 3-sided in cross-section, mostly smooth except just below the spikes. Stems may elongate to 40 inches at maturity and are longer than the leaves. Not all plants produce flowering stems but vegetative shoots are few. Plants are loosely clump forming.

Fruit: Fruit type: seed_without_plume

[close-up of maturing spikes] Fruit develops in late spring to mid summer, the spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are ascending to somewhat spreading and mostly crowded on the spike. Each spike contains 25 to 80 fruits.

[photo of perigynia, scale and developing achene]   Pistillate scales are lance to egg-shaped, translucent whitish to brown-tinged with a green or pale midrib drying to brown, mostly pointed at the tip, 2.9 to 3.5 mm long, usually just reaching the base of the perigynia beak. Perigynia are 3.3 to 5 mm long, 1.8 to 3 mm wide, light green to light reddish-brown at maturity, hairless, distinctly veined on the front, veinless or obscurely veined on the back, flattened, not inflated, the body oval to nearly round, rounded at the base, tapered to a beak .7 to 1.6 mm long, and has a translucent, whitish, papery wing .4 to .8 mm wide around the edges that is more or less the same width all the way to the base. Achenes are lens-shaped, brown at maturity, 1.3 to 1.7 mm long, .8 to 1.3 mm wide, oblong-elliptic, distinctly longer than wide; the distance from the tip of the achene to the tip of the beak is 1.6 to 2.6 mm.


Carex molesta is an occasional to common sedge in the southern half of the state, mostly from the Minnesota River Valley south, usually in the moist soils of open meadows, low prairies, river banks and woodland edges.

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 molesta is a member of the Ovales section, a notoriously difficult group. Some common traits are: usually clump forming, basal sheaths brown and somewhat fibrous, leaves V-shaped when young; 2 to 20 stalkless spikes all at the stem tip and crowded or not, spikes usually all pistillate at the tip and staminate at the base (gynecandrous), lowest bracts scale-like usually with a bristle tip, pistillate scales blunt to pointed at the tip and sometimes awned; perigynia erect to spreading, hairless, veinless to conspicuously veined on one or both surfaces, flat, beaked, usually with a translucent, papery wing; achenes lens-shaped.

Some traits to look at in Ovales are whether spikes are all crowded at the tip or more loosely arranged, whether the inflorescence is nodding or mostly erect, the shape of the spike (round vs. elliptic vs. club-shaped), the size and shape of the perigynia particularly the body (e.g. round vs. elliptic), the width of the wing and whether it extends all the way to the base, whether there are distinct veins on one or both sides of the perigynia, the length of the pistillate scale relative to the perigynia, the shape of the achene, leaf width, and whether sheaths are papillose, but strong magnification (30x or more) is required to see this. Habitat can also be a factor, and a metric scale is essential since fractions of millimeters make a difference.

Carex molesta is distinguished from other Minnesota Ovales species by 2 to 5 spikes (rarely 6), spikes usually crowded together at the stem tip and mostly globular in shape, rounded at the base with few staminate flowers, the inflorescence less than 1 inch long; perigynia 3.3 to 5 mm long (usually less than 4.5), the body oval to nearly round, distinctly veined only on one side and winged to the base, the wing .4 to .8 mm wide and more or less the same width all the way to the base. The distance from the tip of the achene to the tip of the beak is 1.6 to 2.6 mm. It is usually found in moist soil but not always.

Carex molesta is most similar to C. bicknellii, C. merritt-fernaldii, and C. brevior. C. bicknellii is strongly veined on both sides of the perigynia; it and C. merritt-fernaldii both have papillose sheaths, which C. molesta lacks, and more irregular wings that are commonly a bit jagged on the upper half or so. C. molesta is more likely to be confused with C. brevior, which may have up to 7 spikes that are not as crowded, usually with more staminate flowers per spike so the base is more tapered, and is usually in drier soils; when there is overlap on these characteristics check the achene—C. brevior will be broadly egg-shaped to nearly round where C. molesta is proportionately narrower, distinctly longer than wide.

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More photos

Photos by K. Chayka taken in Carver, Dodge and Yellow Medicine counties. Photos by Peter M. Dziuk taken in Fillmore County.


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