Carex foenea (Straw Sedge)

Plant Info
Also known as: Hay Sedge, Bronze-Head Oval Sedge, Dry-spike Sedge, Bronze Sedge
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; dry to moist sandy or rocky soil; roadsides, forest edges, gravel pits, rock outcrops, cliffs
Fruiting season:June - July
Plant height:12 to 48 inches
Wetland Indicator Status:GP: UPL MW: UPL NCNE: UPL
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Spikes: Flower shape: indistinct Cluster type: spike

[photo of spike cluster] 4 to 10 spikes each 7 to 25 mm (to 1 inch) long, loosely arranged at the tip of the stem, the inflorescence (group of spikes) nodding, bent or arching and 1 to 3 inches long. All spikes are stalkless, erect to ascending, usually rounded at the tip and tapering at the base, club-shaped to elliptic in outline, with staminate (male) flowers at the base and pistillate (female) flowers at the tip (gynecandrous). At the base of the lowest spike is a scale-like bract that sometimes has a short, bristle-like tip.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of sheath and ligule] Leaves are alternate with 3 to 6 leaves on the lower half of the stem, up to 12 inches long, 2 to 4 mm wide, flat, hairless, rough-textured near the tip, shorter than the flowering stems. Stem leaf sheaths tightly wrap the stem and are translucent whitish on the front or green and white mottled nearly to the tip; the membranous tip extends slightly above the leaf base and is concave to U-shaped across the top edge. Sheaths are covered in minute bumps (papillose) at least near the tip. The ligule (membrane where the leaf joins the sheath) is about as long as wide.

[photo of basal sheaths] Bases are wrapped in a brown sheath that may be somewhat fibrous, with old leaves often persisting to the next season. Stems are hairless, erect to ascending, 3-sided in cross-section, mostly smooth except just below the spikes. Stems may elongate to about 40 inches at maturity and are longer than the leaves. Plants are clump forming from a mix of vegetative and flowering stems.

Fruit: Fruit type: seed_without_plume

[close-up of maturing spike] Fruit develops in late spring to mid summer, the spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are erect to ascending and not usually tightly crowded on the spike. Each spike contains numerous fruits.

[photo of perigynia, scale and achene] Pistillate scales are lance-shaped, translucent brown-tinged with a green or pale midrib drying to brown, tapering to a sharply pointed tip, as long as and slightly narrower than the perigynia, mostly covering it. Perigynia are 3.3 to 5 mm long, 1.7 to 2.5 mm wide, green to golden to brown at maturity, hairless, distinctly 4 to 9-veined on the front, veinless or unequally veined over the achene on the back, flattened, not inflated, the body lance-oval, tapering at the base, tapering to the beak, and has a wing .2 to .4 mm wide around the edges that does not extend to the base and is commonly obscure until the perigynia dries down. Achenes are lens-shaped, brown at maturity, 1.3 to 2.1 mm long, 1.2 to 1.7 mm wide, narrowly egg-shaped to oblong-elliptic, longer than wide; the distance from the tip of the achene to the tip of the beak is 1.7 to 2.5 mm.

Notes:

Carex foenea, formerly Carex aenea, is an occasional sedge in north-central and northeast Minnesota, most often found in dry, sandy or rocky places. Habitats include the cracks and crevices of cliffs and bluffs, rock outcrops, rocky shores, sandy hillsides, roadsides, gravel pits, and clearings in Jack pine forests. It often appears after disturbance such as fire or a clear-cut.

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 foenea 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 foenea is distinguished from other Minnesota Ovales species by widest leaves less than 3.5 mm; sheaths papillose at least near the tip; 4 to 10 spikes all loosely arranged at the stem tip in a nodding, bent or arching inflorescence (rarely straight) 1 to 3 inches long; spikes mostly club-shaped, tapered at the base, perigynia erect to ascending; pistillate scales as long as and nearly as wide as the perigynia; perigynia 3.3 to 5 mm long, the body oval to egg-shaped, distinctly 4 to 9-veined on the front, veinless or unequally veined over the achene on the back, winged nearly to the base, the wing .2 to .4 mm wide though may be obscure on immature plants. The distance from the tip of the achene to the tip of the beak is 1.7 to 2.5 mm. The pistillate scales as long as the perigynia and the loosely arranged perigynia in a nodding or arching inflorescence are key to an ID.

The pistillate scales as long as the perigynia is a trait shared with other Minnesota Ovales sedges, notably C. adusta, C. praticola, C. xerantica and C. tenera, none of which have papillose sheaths. Of these, C. praticola and C. tenera also have a nodding, bent or arching inflorescence, but C. praticola has larger perigynia (4.5 to 6.5 mm long) and C. tenera is primarily found in moist soil. C. adusta spikes are more tightly arranged at the stem tip and its achenes are much larger, to 2.5 mm long and 2 mm wide. C. xerantica perigynia are mostly appressed on their spikes, and its habitat is primarily the dry prairie of northwest Minnesota. The nodding inflorescence is a trait shared with some other Ovales sedges as well, but the pistillate scales on those will be consistently shorter than the perigynia.

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More photos

Photos by K. Chayka and Peter M. Dziuk taken in Cook and Lake counties.

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