Eriophorum gracile (Slender Cottongrass)

Plant Info
Also known as:
Genus:Eriophorum
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; wet, peaty soil; bogs, conifer swamps, fens, wet meadows, wet ditches, shores
Fruiting season:June - July
Plant height:8 to 24 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] Two to 5 stalked spike clusters all arising from the tip of the stem, with numerous flowers spirally arranged on a spike. Spikes are generally oval when flowering, becoming more cone to fan-shaped in fruit. Stalks are of varying lengths to 1+ inch long, erect to 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 bract] A single, erect, leaf-like bract, up to about 1 inch long, is at the base of the lowest stalk; the bract is commonly dark brown to blackish at the base and does not usually over-top the spikes. Each flower is subtended by a single scale, 3 to 4 mm long, lance to egg-shaped, blunt to pointed at the tip, gray to blackish at least on the tip end and along the thin, translucent edges, with a prominent midrib, the lowest scales with 2 to 4 lateral veins and the upper scales on a spike more weakly veined.

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

[photo of upper leaf and sheath] Leaves are few, alternate, 1 to 2 mm wide, 3-sided but channeled for most of their length, triangular in cross-section towards the tip. The lower leaves are up to 12 inches long but the uppermost leaf is only up to 1½ inches long and shorter than its sheath. Sheaths tightly wrap the stem and are green drying to brown, the uppermost sheath up to 2 inches long. Stems are very slender (less than 1 mm diameter), single, unbranched, erect to flopping, weakly 3-sided to nearly round in cross-section, hairless and smooth. Plants form loose colonies from slender rhizomes.

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

[photo of achene with bristles] The bristles around the base of a flower elongate with maturity, becoming 3/8 to ½ inch (to 15mm) long, and are white.

[photo of scales and achenes (without bristles)] Achenes (seeds) are 1.5 to 3 mm long, brown, 3-sided in cross-section, narrowly elliptic in outline but usually widest above the middle.

Notes:

Eriophorum gracile is an occasional sedge of open, wet bogs and conifer swamps, usually in peaty soils. 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. gracile is the smallest of the group, identified by its loose colonies, slender and smooth stem, leaves less than 2mm wide, the uppermost leaf blade usually less than 1½ inches long and shorter than its sheath, a single short leaf-like bract, and 2 to 5 slender-stalked spikes, at least some of which are typically nodding in fruit. Scales and the base of bracts tend to be gray to blackish, but this is variable.

E. tenellum is most similar but is distinguished by its uppermost leaf blade longer than the sheath (over 2 inches), and rough-textured stem especially on the upper stem; it also blooms about 2 weeks later and is a slightly larger plant, but sizes of the two overlap so is not always the case. Most references note color differences with the scales and bracts (usually blackish for E. gracile and reddish-brown for E. tenellum), but these are rather variable on both species (both can be brown with some black) and we don't think they are reliable distinctions in the field. E. angustifolium and E. viridicarinatum both are more robust plants with 2 or more leaf-like bracts and leaves wider than 2mm that are more or less flat at the base.

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More photos

Photos by K. Chayka taken in Carlton County. Photos by Peter M. Dziuk taken in Carlton, Lake and St. Louis counties.

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