Spikes:

6 to 15 spikes each 4 to 8 mm (to ~1/3 inch) long, all at the tip of the stem, overlapping and usually tightly crowded, the inflorescence (group of spikes) up to about 1½ inches long, usually erect, occasionally slightly nodding. All spikes are stalkless, ascending to spreading, rounded at the tip, rounded at the base, round to oval in outline, with staminate (male) flowers at the base and pistillate (female) flowers at the tip (gynecandrous). Staminate flowers are few so spikes are more globular than club-shaped, and sometimes the lowest spikes are slightly more separated than those above. At the base of the lowest spike is a scale-like bract with a bristle-like tip that may be longer than the spike but does not overtop the terminal spike.

Leaves and stems:

Leaves are alternate with 4 to 6 leaves on the lower half of the stem, up to 16 inches long, 3 to 7 mm wide, flat, hairless, rough along the edges especially near the tip, and commonly bright green especially in sunny locations. The uppermost leaves may rise slightly above the flowering stem but are more often about equal to the stem tip. Stem leaf sheaths are mostly green nearly to the tip, the whitish translucent tip extends above the leaf base and is U- to V-shaped across the top edge. Sheaths loosely wrap the stem especially at the tip, the leaf midvein and edges becoming continuous wings or ridges down the sides and back of the sheath. The ligule (membrane where the leaf joins the sheath) is longer than wide.

Bases are wrapped in a brown sheath that may be somewhat fibrous, with old leaves often persisting to the next season. Stems are hairless, mostly erect, 3-sided in cross-section, mostly smooth except just below the spikes. Stems may elongate to 40 inches at maturity and are longer than most leaves. Plants are clump forming from a mix of flowering and vegetative shoots. Late in the season, old prostrate stems may form buds at the nodes that take root, forming new plants the following year.

Fruit:

Fruit develops in early to mid summer, the spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are tightly crowded, those at the base of a spike are reflexed to spreading, becoming ascending farther up the spike. Each spike contains numerous fruits.

Pistillate scales are lance to egg-shaped, translucent whitish to brown-tinged with a green or pale midrib that does not extend all the way to the tip, mostly pointed at the tip, 1.6 to 2.3 mm long, half to about ¾ as long as the perigynia. Perigynia are 2.6 to 4 mm long, 1 to 1.7 mm wide, light green to straw-colored to light reddish-brown at maturity, hairless, 3 to 6-veined on the front, 2 to 6-veined on the back (may be more obscure), flattened, not inflated, the body elliptic to egg-shaped, tapering the base, tapered to a beak .7 to 1.6 mm long, and has a translucent, whitish, papery wing .1 to .2 mm wide around the edges that is widest above the achene and abruptly narrows at about the middle of the perigynia body; the wing typically becomes rather wavy with maturity. Achenes are lens-shaped, brown at maturity, 1.2 to 1.5 mm long, .6 to .8 mm wide, oblong-elliptic, distinctly longer than wide; the distance from the tip of the achene to the tip of the beak is 1.5 to 1.8 mm.

Notes:

Carex cristatella is a common sedge, found in wet ditches, floodplain forest, shores, stream and river banks, swales, wet meadows, swamps and marshes across the state. It tolerates full sun as well as near full shade.

Carex is a large genus, with over 600 species in North America and 150+ in Minnesota alone. They are grouped into sections, the species in each group having common traits. Carex cristatella is a member of the Ovales section, a notoriously difficult group. Some common traits are: usually clump forming, basal sheaths brown and somewhat fibrous, leaves V-shaped when young; 2 to 20 stalkless spikes all at the stem tip and crowded or not, spikes usually all pistillate at the tip and staminate at the base (gynecandrous), lowest bracts scale-like usually with a bristle tip, pistillate scales blunt to pointed at the tip and sometimes awned; perigynia erect to spreading, hairless, veinless to conspicuously veined on one or both surfaces, flat, beaked, usually with a translucent, papery wing; achenes lens-shaped.

Some traits to look at in Ovales are whether spikes are all crowded at the tip or more loosely arranged, whether the inflorescence is nodding or mostly erect, the shape of the spike (round vs. elliptic vs. club-shaped), the size and shape of the perigynia particularly the body (e.g. round vs. elliptic), the width of the wing and whether it extends all the way to the base, whether there are distinct veins on one or both sides of the perigynia, the length of the pistillate scale relative to the perigynia, the shape of the achene, leaf width, and whether sheaths are papillose, but strong magnification (30x or more) is required to see this. Habitat can also be a factor, and a metric scale is essential since fractions of millimeters make a difference.

Carex cristatella is distinguished from other Minnesota Ovales species by widest leaves 4 to 7 mm wide, loose sheaths that are winged or ridged down the sides and back (continuous with the leaf midvein and edges); 4 to 15 spikes usually crowded together at the stem tip and mostly globular in shape (more oval in larger spikes), rounded at the base with few staminate flowers, the inflorescence up to 1½ inches long, lowest perigynia on a spike widely spreading to reflexed; pistillate scales shorter than the perigynia and the midvein not reaching the tip; perigynia 2.6 to 4 mm long, the body oval-elliptic, veined on both sides (sometimes faintly) and winged above the base, the wing .1 to .2 mm wide, widest above the achene and becoming wavy around the edge; pistillate scales shorter than the perigynia. The distance from the tip of the achene to the tip of the beak is 1.5 to 1.8 mm. It is usually found in moist to wet soil; the foliage is commonly bright yellow-green especially in sunny locations. It is one of the later blooming Carex species, just starting to flower when many others have maturing fruit.

The loose, winged sheaths and prostrate stems rooting at the nodes are traits shared with Carex projecta and Carex tribuloides and when fruiting stems are not present they can be very difficult to distinguish. The spikes of both are more club-shaped to elliptic than C. cristatella, the lowest perigynia in a spike are usually ascending, not widely spreading to reflexed. C. projecta spikes are more loosely arranged in a nodding inflorescence, and C. tribuloides spikes are not as tightly crowded.

The round spikes crowded at the stem tip may be confused with C. molesta or C. bebbii, both of which have tight sheaths, widest leaves usually not more than 4 mm, perigynia are winged to the base (though the wing may be quite narrow), wings are not wavy, and the perigynia at the base of a spike are mostly ascending, not widely spreading to reflexed. C. molesta usually has only 3 or 4 spikes (max 6); C. bebbii commonly has about 6 spikes (max 14) that are more oval, often distinctly longer than wide.