Schoenoplectus acutus (Hard-stem Bulrush)

Plant Info
Also known as: Hard-stem Club-rush
Genus:Schoenoplectus
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; wet; lake and pond shores, wet ditches, fens, calcareous to brackish marshes
Fruiting season:July - September
Plant height:3 to 9 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: panicle Cluster type: spike

[photo of spike clusters] Branching cluster at the top of the stem, usually open, sometimes compact, with 3 to 40 spikelets (flower clusters) some single and others grouped in 2 to 8 at the tips of stiff stalks. Spikelets are 10 to 17 mm long (3/8 to 2/3 inch), elliptic-cylindric, pointed at the tip, reddish to orange-brown, with 8 or more florets spirally arranged. Florets are perfect (both male and female parts) each with a 2-parted style and subtended by a single scale. At the base of the cluster is an erect bract 3/8 to 3½ inches long that is C-shaped in cross-section and appears to be a continuation of the stem.

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

[photo of emergent part of stem base] 3 or 4 leaves are near the base of the stem; only the upper 1 or 2 may have a blade longer than the sheath. Sheaths are often reddish at the base, deeply V-shaped at the tip, the membranous front splitting and becoming coarsely fibrous with age. Stems are erect, round in cross-section, dark olive green, firm and not much spongy when gently squeezed. In cross-section, numerous air cavities are seen, each up to about .5 mm in diameter. Plants form colonies from thick rhizomes.

Fruit: Fruit type: seed without plume

[photo of scales and achenes] Fruit develops in summer, the mature achenes (seeds) dropping off individually leaving the persistent scales behind. Scales are 3 to 4 mm long, 2 to 3 mm wide, green when young turning reddish to orange-brown to straw-colored, variably covered in tiny spines that are red at the base giving a spotted appearance (magnification recommended), generally egg-shaped, notched at the tip with a short, straight to contorted awn. Scale edges are a bit ragged with thick, contorted hairs. Achenes are 2 to 3 mm long, 1.2 to 1.7 mm wide, flat on the back and rounded on the front (plano-convex), urn-shaped in outline, gray-brown and smooth. Surrounding the base are 6 barbed, light brown bristles that are all about the same length and about as long as the achene.

Notes:

Schoenoplectus acutus, formerly Scirpus acutus, is a common wetland species, often found in standing water up to 5 feet deep along lake and pond margins, and may form dense stands. It closely resembles two other Minnesota Schoenoplectus species: Schoenoplectus heterochaetus and Schoenoplectus tabernaemontani. All share the common traits of a round stem, not much for leaves, and a terminal cluster with an erect bract that appears to be a continuation of the stem. S. acutus is distinguished by a firm stem that is not easily compressed when gently squeezed, the stiffly stalked spikelet cluster with up to 40 spikelets, some spikelets single and others grouped 2 to 8, florets with 2-parted styles, distinctly red spotted scales (magnification recommended), plano-convex achenes with (usually) 6 bristles all about the same length and about as long as the achene.

By comparison, S. heterochaetus has spikelets that are almost always all single, occasionally paired, scales with few red spots, florets with 3-parted styles, achenes that are more distinctly 3-sided with 4 bristles, 2 of which are usually much reduced in size. S. tabernaemontani spikelets are mostly solitary with some in groups of 2 to 4, scales are not usually red-spotted, and the stem is a lighter blue-green, quite spongy and easily compressed when gently squeezed. S. acutus hybridizes with both and intermediates may be found when both parents are present. Good luck with those! There are two recognized varieties of S. acutus: var. occidentalis is a western species that is more densely flowered (to 190 spikelets), some or most florets have 3-parted styles, and has a more spongy stem with larger air cavities; var. acutus is found across the northern half of the US into Canada and is described above.

Compare these with other Bulrush species, which may differ by their 3-sided stems, spreading leaf-like bracts, leafier stems, globular clusters of numerous small spikelets, or other traits not as above.

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More photos

Photos by K. Chayka taken in Becker, Hubbard and Lake counties. Photos courtesy Peter M. Dziuk taken in Aitkin and Lake counties. Photos courtesy Steve Eggers taken in Aitkin County.

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