Carex rossii (Ross' Sedge)

Plant Info
Also known as:
Genus:Carex
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Status:
  • State Threatened
Habitat:part shade, sun; dry, rocky soil; cliffs, bluffs
Fruiting season:May - June
Plant height:2 to 10 inches
Wetland Indicator Status:none
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 spikes] Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to 13 mm (½ inch) long at the tip of the stem. Just below the staminate spike are 1 to 4 pistillate spikes, each up to 6 mm (¼ inch) long, short-stalked to stalkless, near the staminate spike but not usually tightly crowded. There are also 1 or 2 erect, short-stalked, all-pistillate spikes near the base of the stem.

[photo of upper spikes and bracts] At the base of lowest non-basal spike is a leaf-like bract that overtops the terminal spike. Bracts become shorter as they ascend the stem.

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

[photo of basal sheaths] Leaves are basal and alternate, mostly near the base, .8 to 2.5(4) mm wide, erect to spreading, shorter or longer than the flowering stem, with old leaves persisting to the next season. The ligule (membrane where the leaf joins the sheath) is wider than long. Bases are wrapped in a reddish brown to purple sheath that may be somewhat fibrous. Stems are erect to ascending, slender, weakly 3-sided, and mostly smooth except on the upper stem. Stems may elongate up to 12 inches at maturity but usually remain shorter than the longest leaves. Plants form loose to dense clumps from short, stout rhizomes.

Fruit: Fruit type: seed without plume

[photo of maturing spikes] Fruit develops in late spring, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Each pistillate spike contains 2 to 15 fruits, the perigynia erect to ascending, overlapping and crowded on the spike.

[photo of perigynia, scale and achene] Pistillate scales are 2.9 to 5.7 mm long, pale to dark reddish-brown with whitish edging, egg-shaped tapering to a pointed tip, sometimes the midrib extending to a short awn, and usually shorter than the perigynia. Perigynia are 3.1 to 4.5 mm long, 1.2 to 1.5 mm wide, sparsely to moderately hairy, 2-ribbed, light green to brownish at maturity, the body oval-elliptic and round in cross-section, the base initially spongy but shriveling to a stalk-like structure (stipe), and abruptly tapering to a straight or slightly bent green beak .9 to 1.7 mm long that has 2 teeth at the tip. Achenes are 1.9 to 2.4 mm long, 1.3 to 1.7 mm wide, oval to round in outline, round to weakly 3-sided in cross-section, and mature to brown.

Notes:

Carex rossii is a rare sedge in Minnesota, disjunct from the main populations in Canada and the western US. According to the DNR, MN populations are all on cliffs, talus slopes and ridge tops, in the shallow soils of rock crevices and ledges. It was listed as a state Threatened species in 2013 due to its rarity, specific habitat requirements, and threats from human activities including logging and recreational uses such as rock climbing and hiking.

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 rossii is in the Acrocystis section (formerly Montanae); some of its common traits are: mostly dry habitat, hairless leaves, basal sheaths typically fibrous, small spikes often tightly clustered, terminal spike staminate, perigynia typically hairy, perigynia with 2 small teeth at the tip of the beak, achenes 3-sided to round in cross-section.

Carex rossii is distinguished by the combination of: clump-forming, red basal sheaths that are not much fibrous, widest leaves usually less than 3 mm wide, single terminal staminate spike, usually a pistillate spike near the plant base, the lowest non-basal spike with a leaf-like bract that overtops the terminal spike, pistillate scales shorter than the perigynia and may be short-awned, hairy perigynia 3.1 to 4.5 mm long with an oval-elliptic body and straight or bent beak to .4 mm long.

Carex rossii is one of a group of 4 members of Acrocystis that have pistillate spikes at the base, the others are Carex deflexa, Carex tonsa, and Carex umbellata. Of these 4, C. deflexa and C. rossii both have leaf-like bracts at the base of the lowest non-basal spike and pistillate scales shorter than the perigynia, where the other two have bristle-like bracts and scales about as long as the perigynia. C. deflexa perigynia are smaller, not more than 3.1 mm long, with a round body and shorter beak. Also similar is Carex peckii, which lacks basal spikes, the lowest bract does not overtop the terminal spike, its fruiting stems are usually longer than the leaves, and perigynia have a shorter beak.

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More photos

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

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