Carex crus-corvi (Raven's-foot Sedge)
|Also known as:|
|Habitat:||part shade, sun; wet; river banks, floodplain forest, wet meadows, marshes|
|Fruiting season:||July - August|
|Plant height:||16 to 36 inches|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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A cluster 4 to 8 inches long at the top of the stem, compound with 15 to 25 distinct branches, the lower branches longer than the upper, and 1 to several spikes on each branch. Branches are mostly erect and overlapping but not tightly crowded except near the tip, though the lowest branch may be farther separated. All spikes are alike with staminate (male) flowers at the tip and pistillate (female) flowers at the base (androgynous). At the base of each spike is a bristle-like bract, the lowest bract longest and may be longer than the associated branch but does not over-top the terminal spike; bracts become shorter as they ascend the stem and are obscure in the uppermost spikes.
Leaves and stems:
Leaves are basal and alternate, mostly near the base, 5 to 10 mm wide, mostly longer than the flowering stems. Stem leaf sheaths are straight across to concave at the tip, smooth (not wrinkled) on the front, snugly wrap the stem, fragile and easily torn, translucent whitish and variably covered in reddish to purplish dots, especially along the edges and near the tip. The ligule (membrane where the leaf joins the sheath) is wider than long and rounded at the tip. Leaves are hairless and V-shaped in cross-section when young. Bases are wrapped in a brown sheath that persists to the next season and may become fibrous. Stems are erect to ascending, strongly 3-sided with narrow wings, stout but spongy and easily compressed, rough textured at least on the upper stem, elongating up to 36 inches at maturity. Plants are clump-forming and not colony-forming.
Fruit develops in late spring through early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Pistillate spikes each contain 8 to 15 fruits that are crowded and spreading in all directions, giving a spiky appearance.
Pistillate scales are narrowly egg-shaped, translucent whitish to pale brown with a green midrib, tapering to a pointed tip, not awned, and are much shorter than the perigynia. Perigynia are 6 to 8 mm long, 1.5 to 2.2 mm wide, yellowish to brown at maturity except paler at the base, obscurely 5-veined on the back, distinctly 10 to 12-veined on the front, hairless, not inflated but with a disk-shaped spongy extension on the front at the base, flattened on the back side, widest near the base, the base abruptly tapered to a short stalk-like structure (stipe), the tip abruptly tapering to a toothed beak to 4.5 mm long (longer than the body) and is finely toothed along the edges. Achenes are up to 2.5 mm long and 1.4 mm wide, flattened lens-shaped, egg-shaped in outline, and mature to brown.
Carex crus-corvi reaches the northwestern fringe of its range in Minnesota, though it has not been seen in the state since 1926 and is assumed extirpated. According to the DNR, it's only been recorded here twice, both times in the Mississippi River floodplain. It was listed as a Special Concern species in 1996 but de-listed in 2013 after biological surveys failed to locate any populations. It is likely disrupting the natural fluctuations in the river's water levels by the lock and dam system has destroyed its habitat. It is currently listed as Endangered in Wisconsin, found there along ephemeral woodland ponds.
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 crus-corvi is in the Vulpinae section; some of its common traits are: clump forming, stems usually spongy, basal sheaths fibrous or not, sheath fronts cross-wrinkled (rugose) or not, leaves hairless and V-shaped in cross-section when young, spike clusters branched (compound) or not (simple) and often crowded, 4 to 20 stalkless spikes, terminal spike with staminate flowers at the tip (androgynous), lateral spikes androgynous or all pistillate, perigynia twice or more as long as wide, widest at/near the base, the base rounded with spongy tissue, tapered at the tip to a toothed beak, flattened lens-shaped achenes. Several of these traits are shared with the Phaestoglochin and Multiflorae sections; both have perigynia widest near the middle and usually less than twice as long as wide, firm stems, and the former usually has more than 15 spikes.
Carex crus-corvi should not be confused with any other sedge in Minnesota. The branched cluster and long-beaked perigynia with a spongy, disk-like base is unique among Minnesota sedges. If you find this in the wild, you have come upon something very special. We'll keep looking ourselves, because you never know...
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Photos by K. Chayka and Peter M. Dziuk taken in the garden.
Have you seen this plant in Minnesota, or have any other comments about it?