Carex retrorsa (Retrorse Sedge)

Plant Info
Also known as: Knotsheath Sedge, Deflexed Bottlebrush Sedge
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; wet; swamps, wet thickets, shores, sedge meadows, wet ditches
Fruiting season:June - August
Plant height:4 to 40 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] Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to 2 inches long at the tip of the stem; occasionally 2 or 3 staminate spikes are present, the secondary spikes smaller and crowding the terminal spike, sometimes with a few pistillate flowers at the base (androgynous). Below the staminate spikes are 3 to 8 pistillate spikes, each up to 2 inches long, erect to ascending, thick cylindric, stalkless to short-stalked. Some pistillate spikes may have a few staminate flowers at the tip. The uppermost pistillate spikes are crowded together just below the terminal spike, except the lowest spike which may be longer stalked and some distance from the spike above it. At the base of each pistillate spike is a leaf-like bract that significantly over-tops the terminal spike; the bract of the lowest spike is 3 to 9 times longer than the inflorescence (group of spikes).

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

[photo of sheath and ligule] Leaves are basal and alternate, 3 to 10 mm wide, the upper stem leaves over-topping the terminal spike. Stem leaf sheaths are concave to U-shaped at the tip, papery translucent whitish-green, and loosely wrap the stem. The ligule (membrane where the leaf joins the sheath) is longer than wide. Leaves are hairless, M-shaped to flat in cross-section, mostly floppy.

[photo of lower stems] Bases are wrapped in a sheath that is dark brown to purplish-brown and is not fibrous. Stems are stout, erect to ascending or sometimes sprawling, 3-sided in cross-section, and smooth. Stems can elongate up to about 3 feet at maturity. Not all plants produce flowering stems. Plants form loose clumps; rhizomes are inconspicuous.

Fruit: Fruit type: seed without plume

[close up of maturing spike] Fruit develops in late spring to mid-summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are widely spreading to angled downward (reflexed, especially near the base of the spike) and tightly packed on the spike. Each pistillate spike contains 20 to 150 fruits.

[photo of perigynia, scales and achene] Pistillate scales are narrowly egg-shaped, white to brown tinged, with a green midrib and a long or short taper to a pointed tip, lack awns, and are 1/3 to about ½ as long as the perigynia. Perigynia are 6 to 10 mm long, 2.1 to 3.4 mm wide, green to yellowish at maturity, hairless, strongly 6 to 13-veined, stiff, inflated, the body oval to nearly round, abruptly tapering to a stalk-like base (stipe), tapering to a slightly angled beak that is about as long as the body, with 2 teeth at the tip. Achenes are 3-sided, maturing to brown, somewhat egg-shaped with a long, persistent style that is contorted near the base.

Notes:

Carex retrorsa is a common sedge of swampy areas, wet thickets, lake and pond shores, and riverbanks throughout Minnesota.

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 retrorsa is in the Vesicariae section; some of its common traits are: clump forming or not, rhizomatous, hairless leaves, basal sheaths brown or red-purple, sheaths often splitting into fibers and forming a ladder shape, sheaths with cross partitions between veins (septate-nodulose), 2 to 10 spikes, terminal spike all-staminate, leaf-like bract subtending the lowest pistillate spike, perigynia mostly ascending to spreading, hairless, mostly egg to teardrop shaped, beaked and toothed, at least slightly inflated, achenes 3-sided in cross-section with a persistent style.

Carex retrorsa is distinguished from all other Minnesota sedges by the combination of: clump-forming, sheaths not fibrous, pistillate spikes erect to ascending, thick, stiff and mostly crowded near the staminate spikes, perigynia widely spreading to reflexed, leaf-like bracts several times longer than the inflorescence, pistillate scales awnless. C. retrorsa somewhat resembles Carex lupulina, which has much larger perigynia (11 to 19 mm long) and the perigynia are all ascending.

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More photos

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

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