Schoenoplectiella purshiana (Weakstalk Bulrush)

Plant Info
Also known as: Weak-stalk Club-rush, Pursh's Tufted Bulrush
Genus:Schoenoplectiella
Family:Cyperaceae (Sedge)
Life cycle:annual
Origin:native
Habitat:sun; sandy, mucky or peaty soil; shores, swamps
Fruiting season:August - October
Plant height:1 to 40 inches
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 spike cluster] One to 12 stalkless spikelets at the top of the stem, subtended by a bract 3/8 to 6 inches long that may be erect or angled away from the spikelets and appearing to be a continuation of the stem, so spikelets seem to be growing out from the side of the stem. Spikelets are 5 to 12 mm (to ~½ inch) long, cone-shaped, blunt to pointed at the tip, pale green to straw colored to orange-brown, with 8 or more florets spirally arranged. Florets are perfect (both male and female parts) each with 3 stamens, a 2 or 3-parted style and subtended by a single scale.

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

[photo of plant base] A single leaf near the plant base is about as long as or shorter than the stem, but is often reduced to a bladeless sheath. Leaves are C-shaped in cross-section and smooth. Sheath fronts are not fibrous. Stems are round in cross-section, .1 to 1 mm in diameter, erect to arching, sometimes prostrate from the base and rising at the tip (decumbent). Stems are typically multiple from the base, forming loose to dense clumps.

Fruit: Fruit type: seed without plume

[photo of scale and maturing achenes] Fruit develops summer into fall, the mature achenes (seeds) dropping off individually. Scales are 2.5 to 3 mm long, up to 2.5 mm wide, pale green to straw-colored to orange-brown, rounded at the tip with an abrupt, sharp point (mucronate). Achenes are 1.5 to 2.2 mm long, urn-shaped in outline, thickly lens-shaped to weakly 3-sided in cross-section, rounded at the tip with a short beak, somewhat rounded to abruptly tapered at the base, .3 to .4 mm wide at the base, faintly textured to smooth on the surface and maturing to brown then blackish. Surrounding the base are usually 6 barbed, light brown to whitish bristles that are most often as long as or longer than the achene, sometimes shorter, rarely absent altogether. Bristles are broadest at the base, evenly tapering to the tip (magnification required).

Notes:

Schoenoplectiella purshiana, formerly Scirpus purshianus then Scheonoplectus purshianus, is an uncommon bulrush that, like many annuals, may not come up in the same place year after year. It typically emerges from sandy or mucky lake shores when water levels recede in summer, or sometimes found in peaty soils and less often swamps. We pursued it for many, many years, but high water levels for several years in a row made it elusive; it finally revealed itself to us in the drought of 2021.

Schoenoplectiella was separated from Schoenoplectus primarily based on being annuals rather than perennials. S. purshiana is distinguished from the only other Schoenoplectiella species in MN (S. smithii) by the combination of: heights of up to 40 inches (often about half that), an erect or angled bract up to 6 inches long and not more than ¼ as long as the stem, achenes usually with 6 bristles that are broadest at the base and evenly taper to the tip (magnification required), the bristles usually about as long as or longer than the achene, sometimes absent altogether. There are 2 varieties of S. purshiana: var. purshiana has bristles and is the more common; var. williamsii lacks bristles but is otherwise identical and, according to Welby Smith's book “Sedges and Rushes of Minnesota”, has only been recorded once in the state.

By comparison, S. smithii is typically a smaller plant, the bract is consistently erect and proportionately longer, sometimes longer than the stem, achenes are .2 to .3 mm wide at the base, bristles number 4 to 6 (occasionally none), are usually 1 to 2 times as long as the achene and are the same width from base to tip. When bristles are absent the width of the achene base may be needed for a positive ID.

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More photos

Photos by K. Chayka taken in Washington County. Photos by Jason Husveth taken in Pine County. S. purshiana robust plant by Shaun Pogacnik, used under CC0 (public domain).

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