Flower:

Loose cluster at the top of the stem, usually compound with several branches arising from the stem tip and several stalked spikelets (flower clusters) arising from the tip of each branch; sometimes clusters are simple (unbranched). Spikelet stalks are of varying lengths, erect to spreading, flattened. At the base of a spikelet cluster are 1 to 3 leaf-like bracts that may be shorter or longer than the associated cluster. Spikelets are lance-shaped in outline, brown to red-brown, 3 to 7 mm long (to ~¼ inch).

Flowers are perfect (both male and female parts), each with 1 or 2 stamens, a 3-parted style, and subtended by a scale. Scales are 1.5 to 2 mm long, egg-shaped, brown to red-brown with a prominent green midrib that typically extends beyond the scale tip.

Leaves and stems:

Leaves are basal, mostly arranged on opposite sides of the stem (2-ranked), ascending to spreading, flat, 1 to 3 mm wide, somewhat rough-hairy along the edges, shorter or longer than the flowering stems. Sheaths are keeled on the back and sometimes fringed with short hairs along the edge near the tip. The ligule (membrane where the leaf meet the sheath) is a fringe of short hairs. Stems are erect to ascending, unbranched, flattened especially near the tip, often rough along the edges, hairless, green, and multiple from the base forming clumps, the stems in a clump often of widely varying lengths.

Fruit:

Achenes (seeds) are .5 to .7 mm long, yellowish to pale brown, 3-sided in cross-section, oval to urn-shaped in outline, the surface smooth to variably warty, especially warty around the base.

Notes:

Fimbristylis autumnalis is an uncommon sedge of moist to wet, sandy or peaty soils, particularly in areas of fluctuating water levels. According to the DNR, in Minnesota it is most common in sedge meadows on the Anoka Sand Plain, on level terrain where the water table is very near the surface. This area has suffered greatly from development as well as encroaching invasive species such as non-native cattails, reed canary grass, and glossy buckthorn. Fimbristylis autumnalis was listed as a Special Concern species in 1996.

It may be mistaken for Bulbostylis capillaris, a species of drier sandy beaches, dunes and rock outcrops, which has narrower, in-rolled (involute) leaves, has only unbranched (simple) clusters and 1 to 7 spikelets, the midrib of the floral scales does not often extend past the scale tip, and achenes are rather larger (about 1 mm), have a more wrinkled texture on the surface, and have a cap-like appendage (tubercle) at the tip. Also similar is the related Fimbristylis puberula, an Endangered species in Minneosta, which is a larger plant (to 20 inches tall), perennial, has involute leaves, larger spikelets (to 10 mm) and a 2-parted style with larger (1 mm) lens-shaped achenes that are pitted on the surface.