Carex trisperma (Three-seeded Sedge)

Plant Info
Also known as:
Family:Cyperaceae (Sedge)
Life cycle:perennial
Habitat:part shade, shade; wet; coniferous swamps, bogs, wet woods
Fruiting season:June - July
Plant height:8 to 28 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: Cluster type: spike

[photo of spikes] 1 to 3 stalkless spikes, separated from each other by ¾ to 1¼ inches. At the base of the lowest spike is a narrow, leaf-like bract that over-tops the terminal spike. All spikes have a few staminate (male) flowers at the base and 1 to 5 pistillate (female) flowers at the tip (gynecandrous). The stem angles at the lowest spike, nodding from that point.

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

[photo of sheath and ligule] Leaves are basal and alternate, mostly near the base, .25 to 2 mm wide, up to 8 inches long, shorter than the flowering stems, mostly floppy. Stem leaf sheaths tightly wrap the stem and are translucent whitish, straight to U-shaped at the tip. The ligule (membrane where the leaf joins the sheath) is as long as or longer than wide. Leaves are hairless, rough along the edges, flat or channeled, V-shaped in cross-section when young. The remains of leaves often persist to the next season.

[photo of basal sheaths] Bases are wrapped in a brown sheath that is not fibrous. Stems are slender, weak, 3-sided and slightly rough textured. Stems often become leaning to arching to nearly prostrate, elongating up to about 2 feet at maturity and are much longer than the leaves. Not all plants produce flowering stems. Plants form loose to dense clumps and may create small colonies from slender rhizomes.

Fruit: Fruit type: seed without plume

[photo of terminal spike with developing fruit] 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. The empty staminate scales persist after fruit has dropped off. Pistillate spikes each contain 1 to 5 fruits that are mostly ascending and not tightly crowded on the stalk.

[photo of perigynia, scale and achene] Pistillate scales are generally egg-shaped, translucent white with a green midrib, tapering to a pointed tip, and are a little shorter than and nearly as wide as the perigynia. Perigynia are 2.5 to 3.7 mm long, 1.5 to 2 mm wide, green to brownish at maturity with many light veins, hairless, loosely wrapping the achene, oval-elliptic, widest near the middle with a long taper to a short beak that has 2 minute teeth at the tip. Achenes are 1.75 to 2 mm long, up to 1 to 1.5 mm wide, flattened lens-shaped, and mature to brown.


Carex trisperma is a circumpolar species, found in Minnesota from the Metro north, primarily in shady, mossy bogs and conifer swamps.

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 trisperma is in the Glareosae section; some of its common traits are: typically clump forming, leaves V-shaped in cross-section when young, leaves hairless and 4mm or less wide, 2 to 10 stalkless spikes, spikes all essentially alike with staminate flowers at the base (gynecandrous), perigynia ascending to spreading and flattened in cross-section, beaked, the beak usually toothed, flattened lens-shaped achenes, typically growing in wetlands.

Carex trisperma is distinguished by the combination of: fine leaves less than 2 mm wide, 2 to 4 spikes that are widely separated from each other, spikes with a few staminate flowers at the base (gynecandrous) and only 1 to 5 perigynia, the lowest spike with a leaf-like bract that over-tops the terminal spike. C. trisperma superficially resembles Carex disperma, which has spikes with staminate flowers at the tip (androgynous), the bract of the lowest spike not over-topping the terminal spike, and perigynia with a rounded tip and minute beak. The arrangement of spikes on the nodding stem also resembles less robust specimens of Carex deweyana, which has rather broader leaves (to 4+ mm wide), larger perigynia (4 to 5mm long) that are minutely serrated along the edges, the bract of the lowest spike does not overtop the terminal spike, and is found primarily in upland woods, less frequently in wetlands. Some references recognize 2 varieties of C. trisperma: var. trisperma, described above, and var. billingsii (or Carex billingsii), a more diminutive form of the species, found in the northeastern US and into Canada.

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More photos

Photos courtesy Peter M. Dziuk taken in Cook and Lake counties. Other photos courtesy Steve Eggers.


Have you seen this plant in Minnesota, or have any other comments about it?

Posted by: Steven Weston - Eagan
on: 2020-09-08 22:04:06

One of approx. 10 species of Carex in my yard. I have a good photo.

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