Eriophorum tenellum (Few-nerved Cottongrass)

Plant Info
Also known as: Delicate Cottongrass, Few-nerved Cotton-sedge
Genus:Eriophorum
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; wet, peaty soil; bogs, conifer swamps, wet meadows, wet ditches, shores
Fruiting season:July - August
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] Two to 7 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 from ¼ 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, ¾ to about 2½ inches long, is at the base of the lowest stalk; the bract is commonly brown to reddish-brown especially at the base and may over-top the spikes. Each flower is subtended by a single scale, 3 to 4.5 mm long, lance to egg-shaped, mostly blunt at the tip, green to reddish-brown to blackish with thin translucent edging, sometimes with a green center that dries pale brown, 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] 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 uppermost leaf is up to 10 inches long, about as long as or longer than its sheath. Sheaths are green and tightly wrap the stem, the uppermost sheath 1 to 3+ inches long. Stems are very slender (less than 1 mm diameter), single, unbranched, erect, weakly 3-sided, hairless but rough-textured especially on the upper stem. Plants form loose colonies from long creeping 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 ¾ inch (to 20mm) long, white to cream-colored.

[photo of lower and mid scales, and achenes (sans bristles) Achenes (seeds) are 2.5 to 3 mm long, brown, 3-sided in cross-section, narrowly elliptic in outline, usually widest at or above the middle.

Notes:

Eriophorum tenellum is an occasional to common sedge of open, wet bogs and conifer swamps, usually in peaty soils, and reaches the southwestern edge of its range in Minnesota. 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. tenellum is identified by its loose colonies, slender and rough-textured stem, leaves less than 2mm wide, the uppermost leaf blade usually longer than its sheath, a single leaf-like bract, and 2 to 7 slender-stalked spikes, at least some of which are typically nodding in fruit. Scales and the base of bracts tend to be mostly reddish-brown, but this is variable.

E. gracile is most similar but is distinguished by its uppermost leaf blade shorter than the sheath (usually under 1½ inches), and smooth stem; it also blooms about 2 weeks earlier and is a slightly smaller 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 and Peter M. Dziuk taken in Carlton and Kanabec counties.

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