Schoenoplectus pungens (Three-square Bulrush)

Plant Info
Also known as: Common Three-square
Genus:Schoenoplectus
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; wet, often in shallow water; lake shores, ponds, streams, wet ditches, fens, marshes
Fruiting season:June - September
Plant height:1 to 6 feet
Wetland Indicator Status:GP: OBL MW: OBL NCNE: OBL
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 flowering spikes] One to 5 (rarely more) stalkless spikelets at the top of the stem, subtended by an erect bract 1 to 8 inches long that appears to be a continuation of the stem, so the cluster seems to be growing out from the side of the stem. Spikelets are 5 to 23 mm (~¼ to nearly 1 inch) long, lance-elliptic, rounded at the tip, orange-brown to purple-brown to straw colored, with florets spirally arranged. Florets are perfect (both male and female parts) each with a 2 or 3-parted style and subtended by a single scale.

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

[photo of lower stem leaves and cross-section] Two to 6 leaves are near the base of the stem, flat to V-shaped in cross-section, the lower leaves reduced to bladeless sheaths, the upper 1 to 3 with a blade longer than its sheath and may be up to 30 inches long and up to 9 mm (~1/3 inch) wide. Sheath fronts are membranous at the tip, often splitting. Stems are erect, firm to somewhat spongy, sharply 3-sided, the sides concave to flat to convex on the lower stem, flat to deeply concave on the upper stem, and may appear somewhat winged. Plants form colonies from firm rhizomes.

Fruit: Fruit type: seed without plume

[photo of spikelet, scales and achenes] Fruit develops from late spring through summer, the mature achenes (seeds) dropping off individually. Scales are 3.5 to 6 mm long, 2 to 3 mm wide, bright to dark orange-brown or purple-brown or straw-colored, lance-elliptic, notched at the tip with a straight to somewhat contorted awn that is longer than the notch lobes. Achenes are 2.5 to 3.5 mm long, 1.3 to 2.3 mm wide, lens-shaped to weakly 3-sided, urn-shaped in outline with a beak up to .5 mm long, smooth and maturing to brown. Surrounding the base are 4 to 8 barbed, light brown bristles that may or may not be equal in length and are usually shorter than the achene.

Notes:

Schoenoplectus pungens, formerly Scirpus pungens, is a common bulrush found in wet places and often in standing water as much as 3 feet deep. In deeper water it may reach heights of 6 feet but in shallower water 3 to 4 feet is common. It resembles 2 other Schoenoplectus species in Minnesota, Schoenoplectus torreyi and Schoenoplectus subterminalis. All 3 share the common traits of a 3-sided stem and 1 to a few spikelets with an erect bract that appears to be a continuation of the stem, so it appears the spikelets grow out from the side of the stem. S. pungens is the most common and robust of the 3, distinguished by a stout stem (to 6mm wide) that is sharply 3-sided and may appear somewhat winged, 1 to 5 spikelets, awned floral scales that are notched at the tip, up to 8 bristles that are as long as or shorter than the achene and may be unequal in length.

By comparison, S. torreyi floral scales are not notched at the tip (or barely so), the stem is more slender, and bristles are mostly similar in length and about as long as or slightly longer than the achene. S. subterminalis is the most diminutive of the 3 species, with a very slender stem (1mm wide or less), single spikelet, and numerous long, thread-like leaves that tend to stay submerged. Some references list 3 varieties of S. pungens, but these are not recognized in Minnesota at this time. S. pungens was once incorrectly lumped with Scirpus americanus (now Schoenoplectus americanus). S. americanus, not known to be in Minnesota, has floral scales with an awn shorter than the notch lobes, the uppermost leaf blade is not usually longer than its sheath, and the floral bract is usually less than 2 inches long.

Compare these with other Bulrush species, which may differ by their round stems, leaf-like bracts, essentially leafless or distinctly leafier stems, globular or branching clusters of numerous small spikelets, or other traits not as above.

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More photos

Photos by K. Chayka taken in Anoka County. Photos courtesy Peter M. Dziuk taken in Ramsey County. Photos courtesy Steve Eggers taken in Mille Lacs County.

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