Carex filifolia (Thread-leaf Sedge)

Plant Info
Also known as:
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; dry; plains, gravel prairies, slopes
Fruiting season:May - June
Plant height:4 to 14 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 flowering spike] A single spike ½ to about 1 inch long at the tip of the stem; the upper half to 2/3 is staminate (male) and the lower portion pistillate (female) (i.e. androgynous). There is no bract at the base of the spike.

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

[photo of leaves] Leaves are mostly basal, less than 1 mm wide, wiry, the edges rolled up forming a slender tube, up to 10 inches long and about as long as or shorter than flowering stems at maturity. Dried leaves and stems can persist to the next season.

[photo of basal sheaths, broken 1 inch above ground] Bases are wrapped in a brown to reddish-brown sheath that becomes fibrous with age. The old stems eventually break off about an inch above ground, leaving the basal sheath stubble. Stems are slender, 3-sided to round in cross-section and can elongate up to 14 inches at maturity. Not all plants produce flowering stems. Plants form very dense clumps from short rhizomes.

Fruit: Fruit type: seed without plume

[photo of mature spike] Fruit develops in mid to late spring, the pistillate flowers forming seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. A spike typically contains 5 to 15 fruits that are appressed to ascending around the stalk.

[photo of perigynia, scale and achene] Pistillate scales are 2.9 to 4.5(6.5) mm long, 1.9 to 4 mm wide, broadly oval to urn-shaped with a rounded to blunt tip, sometimes with a minute point at the tip (mucronate), pale red brown to golden with a broad white translucent edging, are about as long as the perigynia and often completely cover it. Perigynia are 2.8 to 4.8 mm long, 1.4 to 2 mm wide, brown at maturity, fuzzy hairy at least in the upper half, obscurely veined, generally urn-shaped, the body spherical, tapering towards the base, and an abrupt taper to a short, straight, toothless beak. Achenes are 2.2 to 3 mm long, 1.3 to 1.9 mm wide, urn-shaped, 3-sided, and mature to dark brown.

Notes:

Carex filifolia reaches the eastern edge of its range in Minnesota and is typically found in our western counties in open, silty or gravelly soils. The thread-like leaves (hence the very appropriate common name) can create dense tangles.

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 filifolia is the lone member of the Filifoliae section in Minnesota; some of its common traits are: clump-forming, basal sheaths brown and fibrous, leaves very slender and thread-like, a single spike with staminate flowers at the tip (androgynous), perigynia hairy on the upper half and nearly round in cross-section, perigynia beaked without 2 teeth at the tip, achenes 3-sided.

Carex filifolia is distinguished from other Minnesota sedges by the combination of: densely clump forming, leaves less than 1 mm wide, a single spike that is androgynous with up to 15 fruits, and hairy perigynia. It may be mistaken for a member of the Acrocystis section, Carex inops in particular, which has broader leaves (up to 4.5 mm), separate staminate and pistillate spikes, and does not form dense clumps.

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More photos

Photos by K. Chayka taken in the Badlands, South Dakota. Photos courtesy Peter M. Dziuk taken in Pope County and in South Dakota.

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