Carex obtusata (Blunt Sedge)

Plant Info
Also known as: Obtuse Sedge
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Status:
  • State Special Concern
Habitat:part shade, sun; dry sandy or gravelly soil; grasslands, alluvial terraces, beach ridges
Fruiting season:June - August
Plant height:2 to 10 inches
Wetland Indicator Status:none
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 spike] A single spike up to ½ inch long at the tip of the stem, with staminate (male) flowers at the tip and pistillate (female) flowers below (androgynous), all crowded together. A bract at the base of the spike is absent.

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

[photo of sheath] Leaves are basal and alternate, mostly near the base, .5 to 1.5 mm wide, erect to ascending and shorter than the flowering stems. Stem leaf sheaths are concave at the tip, translucent whitish-green. The ligule (membrane where the leaf joins the sheath) is about as long as wide. Leaves are V-shaped in cross-section when young, and hairless though rough-textured along the edges.

[photo of basal sheaths] Bases are wrapped in a reddish-brown to purplish-brown sheath that is not fibrous. Stems are erect, 3-sided, very slender, longer than the leaves. Plants are not clump-forming and typically create colonies from long, purplish-black rhizomes, often in straight lines.

Fruit: Fruit type: seed without plume

[photo of mature spike with blackish perigynia] Fruit develops in late spring to mid-summer, the spike forming a cluster of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. The spike usually contains 1 to 6 fruits, ascending to spreading, congested just below the staminate flowers.

[photo of perigynia, scales and achene] Pistillate scales are broadly egg-shaped with a pointed tip, whitish to pale brown with a tan midvein, about as wide as and as long as or slightly shorter than the perigynia and mostly covering it. Perigynia are 3 to 4 mm long, several-veined (most visible in the lower half), hairless, thick-walled and leathery, shiny reddish-brown turning blackish when mature, oblong-elliptic with a short beak that has 2 small teeth at the tip. Achenes are 3-sided to nearly round in cross-section, generally oval in outline, and more or less fill the perigynia.

Notes:

Carex obtusata is an uncommon sedge of dry, sandy or gravelly prairies and reaches the eastern edge of its range in Minnesota, the largest populations in our northwest counties. According to the DNR, intact prairires of any kind are rare in the state, and sand prairie that hosts C. obtusata is one of the rarest; it was subsequently listed as a Special Concern 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 obtusata is the lone member of the Obtusatae section in North America; some of the section's common traits are: long-rhizomatuous, not clump forming, basal sheaths reddish-brown to purplish-brown and not usually fibrous, leaves hairless and V-shaped in cross-section when young, 1 spike per stem, spike with staminate flowers at the tip (androgynous), perigynia hairless and weakly to distinctly veined, perigynia reddish-brown to black, beaked with 2 small teeth, achenes 3-sided, nearly round in cross-section.

Carex obtusata should not be confused with any other sedge in Minnesota; the combination of small stature, sand prairie habitat, single androgynous spike with shiny, thick-walled, reddish-brown to black perigynia, and rhizomatous growth make it unique in the state.

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More photos

Photos courtesy Peter M. Dziuk taken in Kittson County.

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