Eriophorum viridicarinatum (Green-keeled Cottongrass)

Plant Info
Also known as: Thin-leaf Cotton-sedge, Tassel Cotton-grass,
Family:Cyperaceae (Sedge)
Life cycle:perennial
Habitat:part shade, sun; wet; bogs, conifer swamps, marshes, fens, wet meadows, wet woods, shores
Fruiting season:
Plant height:8 to 36 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

Flower: Flower shape: indistinct Cluster type: spike

[photo of spikes coming into flower] Three to 30 stalked spike clusters all arising from the tip of the stem, with numerous flowers spirally arranged on a spike. Spikes are generally oval-elliptic when flowering, becoming more cone to fan-shaped in fruit. Stalks are of varying lengths from 3/8 to 2+ inches long, mostly nodding. Flowers are perfect (both male and female parts) with 3 stamens, a 3-parted style, and 10 or more straight, smooth, thread-like bristles surrounding the base.

[photo of bracts] The lowest 2 or 3 stalks each have a leaf-like bract, the base usually green, sometimes brown, the longest up to 2¾ inches long and usually over-topping the spikes. Each flower is subtended by a single scale, 4 to 6 mm (to ¼ inch) long, lance to egg-shaped, blunt to pointed at the tip, blackish-green to gray-brown, usually darker at the tip end, with minute teeth along the edges at the tip end, and a prominent midvein that is enlarged at the tip end and extends to the tip of the scale, sometimes a little beyond.

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

[photo of upper sheath] Leaves are few, basal and alternate, 2 to 6 mm wide, up to 12 inches long, more or less flat at the base but triangular in cross-section towards the tip. The uppermost leaf is much longer than its sheath. Sheaths tightly wrap the stem and are green with a narrow band of translucent tissue around the tip edge.

[photo of plant base] Stems are about 1 mm diameter, single or loosely clumped, unbranched, erect, nearly round in cross-section, and hairless. Plants can form colonies from long creeping rhizomes.

Fruit: Fruit type: seed with plume Fruit type: seed without plume

[photo of maturing spikes] The bristles around the base of a flower elongate with maturity, becoming ½ to 1+ inch (to 30mm) long, white to cream-colored.

[photo of scales and achenes] Achenes (seeds) are 2.5 to 3.5 mm long, brown, 3-sided in cross-section, narrowly urn-shaped in outline, widest near the tip.


Eriophorum viridicarinatum is an occasional sedge of bogs, tamarack swamps and wet meadows, found mostly in the northern third of the state. The Cottongrasses in Minnesota are separated into two groups: those with an erect, hemispheric to round seed head, and those with multiple, distinctly stalked, nodding spikes. The latter group includes E. angustifolium, E. gracile, E. tenellum and E. viridicarinatum. E. viridicarinatum is identified by its loose colonies, stems single or loosely clumped, leaves more than 2mm wide and flattish at the base, the uppermost leaf blade usually longer than its sheath, 2 or 3 leaf-like bracts green or brown at the base, 3 to 30 slender-stalked spikes (the most of all MN Cottongrasses) most of which are nodding in fruit, and blackish-green to gray-brown floral scales 4 to 6 mm long with a midrib that is enlarged towards towards the tip and extends to the scale tip, sometimes beyond. The tips of sheaths are green, not darkened.

E. angustifolium is most similar but is distinguished by bracts purple to black at the base, sheaths slightly inflated and usually purplish at the tip, and floral scales 5 to 10 mm long with a midrib that fades away towards the scale tip. E. gracile and E. tenellum are both smaller plants with slender stems less than 1 mm wide, channeled leaves not more than 2 mm wide, a single leaf-like bract, and floral scales not more than 4.5 mm long.

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More photos

Photos by Peter M. Dziuk taken in Beltrami and St. Louis counties.


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