Carex tenuiflora (Sparse-flowered Sedge)

Plant Info
Also known as: Thin-flowered Sedge
Family:Cyperaceae (Sedge)
Life cycle:perennial
Habitat:part shade, sun; wet; calcareous fens, coniferous swamps, bogs, wet woods, floating mats, shores
Fruiting season:June - July
Plant height:4 to 20 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 spikes] 2 to 4 stalkless spikes, all close to each other at the tip of the stem. At the base of the lowest spike is sometimes a narrow, leaf-like bract that may over-top the terminal spike, but the bract is often absent or bristle-like and shorter than the attending spike. All spikes have a few staminate (male) flowers at the base, 3 to 15 pistillate (female) flowers at the tip (gynecandrous) and are up to 15mm (about ½ inch) long.

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

[photo of ligule and outer sheath] Leaves are basal and alternate, mostly near the base, .5 to 2 mm wide, 2 to 6 inches long, shorter than the flowering stems, mostly erect to ascending. Stem leaf sheaths are translucent whitish, concave at the tip. The ligule (membrane where the leaf joins the sheath) is about as long as wide. Leaves are hairless, flat or channeled, V-shaped in cross-section when young.

[photo of brown basal sheaths] Bases are wrapped in a brown sheath that is not fibrous. Stems are slender, weak, 3-sided and slightly rough textured. Stems are initially erect often become leaning to nearly prostrate, elongating up to about 20 inches at maturity and are much longer than the leaves. Not all plants produce flowering stems. Plants form loose to dense clumps from slender rhizomes.

Fruit: Fruit type: seed without plume

[photo of mature spikes, with a long bract] 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 scales persist after fruit has dropped off. Pistillate spikes each contain 5 to 15 fruits that are ascending to spreading and somewhat crowded in an oval to hemispheric cluster.

[photo of perigynia front and back, scale and achene] Pistillate scales are generally egg-shaped, translucent white with a green midrib that dries to brown, tapering to a blunt tip, and are nearly as long and as wide as the perigynia. Perigynia are 2.7 to 3.8 mm long, 1.4 to 1.75 mm wide, hairless, brown at maturity with 13 to 20 darker brown veins, lance-elliptic, tapering to an obscure beak at the tip, and surfaces densely covered in minute white dots (puncticulate). Achenes are 1.75 to 2 mm long, up to 1 to 1.5 mm wide, flattened lens-shaped, and mature to brown.


Carex tenuiflora is a circumpolar species, found primarily in northern Minnesota in mossy bogs, conifer swamps, peatlands and on floating mats, but may also be found in pools along the rocky north shore of Lake Superior.

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 tenuiflora 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 tenuiflora is not easily confused with other sedges; it is distinguished by the combination of: 2 to 4 spikes that are closely clustered at the top of the stem, spikes oval to hemispheric with a few staminate flowers at the base (gynecandrous) and 5 to 15 perigynia, pistillate scales nearly covering the perigynia and translucent white except the midrib, perigynia to 3.8mm long, tapering to an obscure beak and densely covered in minute white dots (magnification required). C. tenuiflora superficially resembles Carex leptalea, which has a single spike with staminate flowers at the tip (androgynous). Of note is that most references state the veins on C. tenuiflora perigynia are obscure, but we disagree: though the veins are not raised, when green the veins are faint but when mature, the coloring makes them really stand out.

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More photos

Photos by K. Chayka taken in Cook County. Photos courtesy Peter M. Dziuk taken in Cook and Lake counties.


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

Posted by: gary - Cook County
on: 2019-11-17 18:37:23

Part of the ground layer flora in a river shore fen (Poplar River upper reach above Screech Lake).

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