Carex leptonervia (Nerveless Woodland Sedge)
|Also known as:||Fine-nerved Sedge|
|Habitat:||part shade, shade, sun; moist to wet; woods, thickets|
|Fruiting season:||June - July|
|Plant height:||6 to 18 inches|
|Wetland Indicator Status:||GP: FAC MW: FAC NCNE: FAC|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to about 2/3 inch long at the top of the stem. Below the staminate spike are 3 or 4 cylindric, erect to ascending, all-pistillate spikes each 1/3 to 7/8 inches long, the uppermost 1 or 2 spikes short-stalked and near the staminate spike but not crowding it, though sometimes over-topping it. Lower pistillate spikes arise singly from the nodes on the upper half of the stem, on erect stalks up to about 3 inches long. Pistillate spikes each have a leaf-like bract at the base of the stalk, the second from the top usually over-topping the terminal spike. The uppermost bract is often shorter and narrower than the lower bracts.
Leaves and stems:
Leaves are basal and alternate, 4 to 12 inches long, 3 to 10 mm (1/8 to 3/8 inch) wide, mostly ascending, and shorter than the flowering stem. Stem leaf sheaths loosely wrap the stem and are papery, translucent whitish. The ligule (membrane where the leaf joins the sheath) is longer than wide. Leaves are hairless, M-shaped in cross-section when young.
Bases are wrapped in a brown sheath that is not fibrous. Stems are 3-sided and winged along the angles, hairless but rough in the upper plant, erect to ascending to sprawling, and may elongate up to 18 inches at maturity. Not all plants produce flowering stems. Plants typically form dense clumps.
Fruit develops in spring through early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Staminate scales are white to light brown with a green midrib and pointed tip. Pistillate spikes have 5 to 14 fruits, the perigynia mostly ascending, sometimes spreading, overlapping but often loosely arranged on the spike.
Pistillate scales are lance-oblong, white to light brown with a green midrib, rounded at the tip with the midrib often extending to a rough-textured awn, and about ¾ as long as the perigynia, excluding the awn. Perigynia are yellowish-green to brown at maturity, 2.2 to 3.2 mm long, 1 to 1.5 mm wide, essentially veinless except for 2 strong ribs, hairless, not much inflated, asymmetrically urn-shaped, tapering to a spongy base, and with an abrupt taper to a toothless, bent or slightly curved beak .3 to 1.1 mm long. Achenes are 1.8 to 2.8 mm long, weakly 3-sided in cross-section, widest near or above the middle, rounded at the tip and tapering at the base.
Carex leptonervia reaches the southwestern edge of its US range in Minnesota. While it is typically a sedge of moist, shaded deciduous or mixed forest, we encountered it in an open area that had been clear-cut some years prior. With more sun, it may have been a bit more robust than average, and maybe it likes a little disturbance, too.
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 leptonervia is in the Laxiflorae section; some of its common traits are: usually densely clump forming, short to long rhizomatous, stems slightly winged along the angles, basal sheaths brown or purple and not fibrous, leaves M-shaped in cross-section when young, leaves hairless, widest leaves 5+ mm, 3 to 6 spikes, terminal spike all staminate, lateral spikes all pistillate, lateral spikes subtended by a long-sheathing leaf-like bract, perigynia hairless, generally urn-shaped and tapering to a spongy base, distinctly 8+ veined and abruptly beaked, achenes 3-sided with 3 stigmas, usually growing in woodlands.
Carex leptonervia is distinguished from other Carex species by the combination of: brown basal sheaths, leaves shorter than the flowering stem, terminal spike all staminate, the uppermost 1 or 2 pistillate spikes near the staminate spike but not crowding it, perigynia asymmetrical with 2 strong ribs (otherwise veinless or obscurely veined), widest above the middle, 2.2 to 3.2 mm long with a bent, toothless beak, and weakly 3-sided achenes.
It is similar to other members of the Laxiflorae section, in particular Carex blanda, which has somewhat larger perigynia (to 4mm long) and leaves longer than the stem, and Carex ormostachya, which has reddish-purple basal sheaths, and both of which have perigynia with more numerous and conspicuous veins, most obvious when dry.
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Photos courtesy Peter M. Dziuk taken in Cook County.
Have you seen this plant in Minnesota, or have any other comments about it?