Carex backii (Back's Sedge)
|Also known as:|
|Habitat:||part shade, shade; dry rocky or sandy soil; forests, thickets, rock outcrops, shaded slopes|
|Fruiting season:||May - July|
|Plant height:||2 to 10 inches|
|Wetland Indicator Status:||none|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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A spike at the top of the stem with 2 or 3 staminate (male) flowers at the tip and pistillate (female) flowers below (androgynous), the staminate portion not more than 3.6 mm (~1/8 inch) long. At the base of each pistillate flower is a leaf-like bract, the lowest one in the spike largest, to 5.5 mm wide and 4 cm (1½ inch) long, wider and much longer than the spike and mostly hiding it, the bracts becoming smaller as they ascend the spike. One or 2 additional spikes on slender, erect stalks may arise from the base of the stem; these are androgynous or all-pistillate. The leaf-like bracts on these lateral spikes tend to be smaller and not as concealing as those on the terminal spike.
Leaves and stems:
Two to 6 leaves are attached at the base, each up to 15 inches long, 1.3 to 6 mm wide, much longer than the flowering stems, hairless, mostly flat. Bases are wrapped in a brown sheath that is not fibrous; some old sheaths may persist to the next season. Stems are slender, erect to ascending, 3-sided, varying in length but under 10 inches tall at maturity and remain much shorter than the leaves. Plants are clump-forming, not colony forming, a clump often appearing somewhat flattened.
Fruit develops in late spring to early summer, the spike forming a cluster of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale; staminate scales may persist on the terminal spike. Each spike contains 2 to 7 fruits, erect to ascending and overlapping.
Pistillate scales are narrowly lance-shaped, green and leaf-like, tapering to a pointed tip, longer and wider than the perigynia, that of the lowest perigynia largest, the uppermost smaller but still usually longer than the perigynia. Perigynia are 4.8 to 6.6 mm long, 1.9 to 3.2 mm wide, 2-veined, green to olive when mature, lance-oval, nearly round in cross-section, somewhat loosely wrapping the achene, abruptly tapered at the spongy base, more gradually tapering to toothless beak 1.9 to 2.9 mm long. Achenes are 2.5 to 3.2 mm long, nearly round in cross-section, rounded at the tip, abruptly tapered at the base, brown at maturity.
Carex backii is an occasional sedge of bluffs, wooded slopes, ravines, and sandy ridges in pine stands. Our own encounters were on moss-covered rock in shady, deciduous woods.
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 backii is in the Phyllostachyae section; some of its common traits are: clump forming, basal sheaths brown and not fibrous, leaves V-shaped in cross-section when young, leaves hairless and much longer than fruiting stems, 1 to 5 spikes, terminal spike with staminate flowers at the tip (androgynous), lateral spikes stalked and androgynous or all-pistillate, lowest sometimes at or near the plant base, perigynia beaked and hairless, 2-veined or obscurely veined, beak toothless, lowest pistillate scales green and leaf-like, achenes 3-sided with 3 stigmas. The leaf-like pistillate scales are unique to species in this section.
Carex backii is one of the three members of the Phyllostachyae section in Minnesota and is distinguished from other Carex species by the combination of: clump-forming, largest leaves to 6 mm wide and much longer than the flowering/fruiting stems, stems of varying lengths and some spikes near the plant base, terminal spike with erect, leaf-like bracts wider than the perigynia, much of the terminal spike hidden by the bracts, perigynia 4.8 to 6.6 mm long. Most similar is Carex saximontana, which has perigynia less than 5 mm long with a shorter, more abruptly tapered beak. The third member of this section, Carex jamesii, has a much longer staminate portion on the terminal spike (to 14mm/½+ inch), periginia up to 7.5 mm long with a more abrupt taper to a slender beak up to 3.8 mm long, and forms denser, leafier mounds in moister, rich forest habitats.
When spikes are absent, Carex backii can resemble Carex pedunculata, with which it may grow side by side. C. pedunculata tends to form more dense clumps with more numerous, persistent old leaves and has red-purple basal sheaths, where C. backii sheaths are brown.
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- Carex backii plant
- Carex backii plant
- Carex backii plants
- Carex backii (left) with Carex pedunculata (right)
- scan of plant
- spike near plant base
Photos by K. Chayka taken in Washington County and in Wisconsin. Photos by Peter M. Dziuk taken in Wisconsin.
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