sterile sedge

not listed

NNR - Unranked

S2 - Imperiled

Threatened

OBL - Obligate wetland

OBL - Obligate wetland

OBL - Obligate wetland

Sterile sedge is a stiffly erect, 4″ to 29″ tall, perennial sedge rising from a very short underground stem (rhizome). It usually forms dense clumps. It is often the dominant species.

Sterile stems are poorly developed and are mostly reduced to basal clusters of leaves. Basal leaves are reduced to nearly bladeless sheaths.

The flowering stem (culm) is sharply three-angled, stiff, hairless, brown at the base, and 4″ to 29″ long, longer than the leaves. It is not winged. The angles are rough to the touch on the upper portion of the stem. Three to five slender stem leaves, arranged in three vertical rows (ranks), appear on the lower third of the culm.

The stem leaves are green, hairless, 3″ to 10″ long, and 1 ⁄32″to ⅛″wide. The leaf blade has a single prominent midvein and is folded like a fan, at least near the base. The margins are rough to the touch. The lower part of each leaf that surrounds the stem (sheath) is thin, papery, and white or nearly white. It is not fibrous. The tip of the sheath is usually concave, sometimes straight across. The lowermost part is brown. The membrane where the leaf meets the stem (ligule) is rounded to broadly angled and 1 ⁄64″ to 1 ⁄16″ long. It is mostly fused to the inner face of the leaf blade but it has a loose margin.

The inflorescence consists of 3 to 8, usually 4, unisexual elongated flower clusters (spikes) at the end of the stem. The spikes are stalkless and are readily distinguished from each other. The upper spikes are crowded together but at least one spike, the lowest, is separate and does not overlap the adjacent spike. The modified leaf (bract) that usually subtends a sedge spike, is missing or inconspicuous and scale-like.

The inflorescences are highly variable. The terminal spike is usually all male (staminate) or all female (pistillate). Some plants have all staminate spikes, sometimes with a few pistillate flowers scattered on some spikes. Some plants have all pistillate spikes, rarely with a few staminate flowers scattered on some spikes. Occasionally, entirely pistillate spikes and entirely staminate spikes will be mixed on the same plant. The common name refers to the fact that some clumps are all staminate, and do not produce seed—hence, sterile.

Staminate spikes are slender, club-shaped, ⅛″ to 9 ⁄16″ long and 1 ⁄32″ to ⅛″ wide. They consist of 6 to 31 flowers in a dense, spiral arrangement. Each staminate flower is subtended by a single egg-shaped, 1 ⁄16″ to ⅛″ long scale. The scale is brown with a green midrib and pale margins. The flower consists of 3 stamens with conspicuous, bright yellow, 1 ⁄32″ to 1 ⁄16″ long anthers. The anthers fall off soon after pollination leaving just the filaments.

Pistillate spikes are much broader, star-like, ⅛″ to ½″ long and 3 ⁄16″ to ¼″ wide. They consist of 5 to 26 flowers. Each pistillate flower is entirely enclosed by a sac-like bract (perigynium) and subtended by a single scale. The scale is egg-shaped, 1 ⁄16″ to ⅛″ long, and brown, with a green midrib and pale margins. It is narrowly pointed and is as long or nearly as long as the perigynium. The perigynium is chestnut brown to blackish, egg-shaped to almost triangular, 1 ⁄16″ to ⅛″ long, and 1 ⁄32″ to 1 ⁄16″wide. It is thickened and spongy at the base and evenly tapered from the body to the tip, not forming a shoulder. It is not winged. The extended tip (beak) is 1 ⁄64″ to 1 ⁄16″long, a third or more of the total length of the perigynium. It is densely and irregularly toothed along the margins. Two white stigmas emerge from a small opening at the tip of the perigynium.

The fruit is a dry, yellowish-brown, egg-shaped to almost circular in outline, one-seeded capsule (achene). It is 1 ⁄32″ to 1 ⁄16″long, much smaller than the perigynium. It matures in June or July and drops from the plant soon after.

4″ to 29″

Calcareous fens, calcareous wet prairies, and spring fens

Mid-May to early August

Sources

2, 3, 4, 5, 6, 7, 28, 29, 30, 84.

Native

Widespread statewide and locally common but rare due to limited habitat

Unlike most plants in the genus Carex, this plant bears male and female flowers on separate plants. This characteristic gives the plant one of its common names, dioecious sedge.

Plant

Spikes