Flower:

Two to 10 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 ¼ to 2+ inches 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.

The lowest 2 or 3 stalks each have a leaf-like bract, the base commonly dark reddish-purple to blackish, the longest up to 4¾ inches long and usually over-topping the spikes. Each flower is subtended by a single scale, 5 to 10 mm (to 3/8 inch) long, lance to egg-shaped, blunt to pointed at the tip, light brown to dark purplish-brown, paler at the tip, with a prominent midvein that fades away before reaching the tip.

Leaves and stems:

Leaves are few, alternate, 2 to 8 mm wide, up to 16 inches long, more or less flat at the base but triangular in cross-section towards the tip. The uppermost leaf is about as long as or longer than its sheath. Sheaths are slightly inflated and green or (frequently) purplish at the tip, with a narrow band of translucent tissue around the tip edge. Stems are about 1 mm diameter, single, unbranched, erect, nearly round in cross-section, and hairless. Plants form loose colonies from long creeping rhizomes.

Fruit:

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

Achenes (seeds) are 2.5 to 3 mm long, brown, 3-sided in cross-section, narrowly elliptic to urn-shpaed in outline, usually widest above the middle.

Notes:

Eriophorum angustifolium is the most common Eriophorum species in Minnesota, found across the state in open, wet places such as bogs, fens, marshes, prairie swales, sedge meadows, and wet ditches, usually in peaty or sandy 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. angustifolium is identified by its loose colonies, leaves more than 2mm wide, flattish leaves, the uppermost leaf blade usually longer than its sheath, 2 or 3 leaf-like bracts purplish to blackish at the base, 2 to 10 slender-stalked spikes, at least some of which are typically nodding in fruit, and brown to purplish floral scales 5 to 10 mm long with a midrib that does not extend to the tip. The tips of sheaths are commonly reddish-purple even on young plants, and later in the season much of the foliage can also turn purplish.

E. viridicarinatum is most similar but is distinguished by its mostly green floral bracts, green sheaths that tightly wrap the stem, and dark green to gray-brown scales with a midrib that is enlarged on the tip end and extends to the scale tip, sometimes to a short awn. 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 less than 5 mm long. There are two recognized subspecies of E. angustifolium: subsp. triste, present in Alaska and northern Canada, is not more than 12 inches tall and has spike stalks rough on all surfaces; subsp. angustifolium, present across northern North America including Minnesota and, has spike stalks smooth or rough only along the angles, and is up to 40 inches tall (though more often 30 inches or less).