Flower:

A single, erect cluster at the tip of the stem, oval-elliptic in flower becoming hemispheric to round in fruit, ¾ to 2 inches long at maturity, with numerous flowers spirally arranged. Flowers are perfect (both male and female parts) with 1 to 3 stamens, a 3-parted style, and 10 or more straight, smooth, white (rarely brownish or reddish), thread-like bristles surrounding the base.

Each flower is subtended by a single scale, though the lowest scales (10 or more) are typically empty. Fertile scales are 5 to 10 mm (to 3/8 inch) long, lance to egg-shaped with a long taper to a sharply pointed tip, widest below the middle, gray-green to gray-black with paler translucent edging and a prominent midvein that does not quite reach the scale tip. There are no leaf-like bracts at the base of the cluster.

Leaves and stems:

Stem leaves are few, basal and alternate, the uppermost 1 to 3 stem leaves reduced to bladeless sheaths that are loose, inflated towards the tip, and green becoming papery brown.

Lower stem leaves are nearly bladeless while leaves of vegetative shoots are 1 mm wide, shorter than to nearly as long as the flowering stem, triangular in cross-section; basal sheaths are persistent and brown. Stems are unbranched, multiple from the base, erect, 3-sided in cross-section, hairless and smooth. Plants form dense clumps, the old stems and sheaths persisting and forming large tussocks.

Fruit:

The white bristles around the base of a flower elongate with maturity, becoming 3/8 to ¾ inch long. Achenes (seeds) are 1.9 to 3.5 mm long, brown, 3-sided in cross-section, urn-shaped in outline, widest near the tip, with an abrupt taper to a minute point at the tip.

Notes:

Eriophorum vaginatum is a common sedge of open, wet places in the northern half of Minnesota, except for our western counties. It reaches the southwestern edge of its US 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 former group includes E. russeolum, E. vaginatum and E. virginicum, which are not difficult to distinguish from each other. Of these three: only E. vaginatum is densely clump-forming, only E. virginicum has multiple spikes with leaf-like bracts, and E. russeolum is neither clump-forming nor does it have leaf-like bracts. There are other, more subtle differences, such as scale color or shape of the achene tip, but those traits are not as immediately obvious.