Carex debilis (Weak Sedge)

Plant Info
Also known as: White-edge Sedge
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; woodlands, deciduous forest, clearings, wet prairies, sedge meadows
Fruiting season:June - August
Plant height:10 to 40 inches
Wetland Indicator Status:GP: OBL MW: FACW NCNE: FACW
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 top of the stem, which usually has a few to several pistillate flowers at the very tip (gynecandrous). Below the staminate spike are 2 to 5 slender-stalked, all-pistillate spikes, widely spaced and arising singly from the nodes with a leaf-like bract at the base of the stalk. The stalk of the lowest spike is longest with the stalks becoming progressively shorter as they ascend the stem, the stalks initially erect to ascending, becoming drooping with maturity. Pistillate spikes are slender and cylindrical, up to about 3 inches long, erect and green at flowering time with white, thread-like styles, and the staminate spike with creamy yellow stamens.

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

[photo of stem sheath and ligule] Leaves are basal and alternate, mostly near the base, 2 to 7 mm wide, as long as or shorter than the flowering stems, becoming arching. Stem leaf sheaths loosely wrap the stem and are papery, translucent whitish. The ligule (membrane where the leaf joins the sheath) is longer than wide. Leaves are M-shaped in cross-section when young, and hairless though slightly rough along the edges or midrib.

[photo of basal sheath] Bases are wrapped in a light tan to green sheath that is not fibrous and is typically tinged red to purple. Stems are slender, 3-sided and mostly smooth except rough in the upper plant. Stems become leaning to arching, elongating up to 3 feet or more at maturity and usually longer than the leaves. Not all plants produce flowering stems. Plants form loose to dense clumps.

Fruit: Fruit type: seed without plume

[photo of mature terminal spike] Fruit develops in late spring through mid-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 10 to 25 fruits that are somewhat loosely arranged on the stalk, spaced 2 to 9 mm apart.

[photo of perigynia, scale and achene] Pistillate scales are oval to lance-oblong, translucent white sometimes tinged chestnut brown with a green midrib that turns brown, blunt to pointed at the tip or the midrib extending to an awn up to .2 mm long, may be hairy around the top edge, and are shorter than the perigynia. Perigynia are green, 5 to 6.2 mm long, 1.1 to 2 mm wide, 2-ribbed with 12 to 20 faint veins, hairless, loosely wrapping the achene, nearly spindle-shaped, the body narrowly lance-elliptic, tapering to the stalkless base, a long taper to the beak, and 2 teeth at the tip. Achenes are 1.9 to 2.5 mm long, up to 1.5 mm wide, 3-sided in cross-section, and mature to golden brown.

Notes:

Carex debilis is found throughout Minnesota in woodlands and open, moist areas.

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 debilis is in the Hymenochlaenae section; some of its common traits are: typically clump forming and forming loose colonies, leaves M-shaped in cross-section when young, spikes long and cylindric and drooping on slender stalks, terminal spike either all staminate or with a few perigynia (usually at the tip, occasionally the base), perigynia round in cross-section, 2-veined, beaked, the beak usually toothed, 3-sided achenes, often growing in woodlands.

Carex debilis is very similar in appearance to two other hairless Minnesota sedges: Carex gracillima, which has beakless perigynia, and Carex arctata, which has an all-staminate terminal spike and perigynia with an abrupt taper to a stipe (stalk-like structure) at the base. C. debilis has been reported to hybridize with other members of its section, though these are not documented in Minnesota. It is a rather variable species but with only two recognized varieties: var. debilis present to our south and east with perigynia up to 9.5 mm long, and var. redgei described above and present in Minnesota.

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More photos

Photos by K. Chayka taken in Anoka and Ramsey counties. Photos courtesy Peter M. Dziuk taken at Blaine Preserve SNA, Anoka County.

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