Scirpus microcarpus (Small-fruited Bulrush)
|Also known as:||Panicled Bulrush, Barber-pole Bulrush, Small-fruited Bulsedge|
|Habitat:||sun; moist to wet; lakes, stream banks, wet ditches, wet meadows, marshes|
|Fruiting season:||July - September|
|Plant height:||2 to 5 feet|
|Wetland Indicator Status:||GP: OBL MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Stiff, open to compact branching cluster at the top of the stem, the main branches straight to arching and more or less radiating in all directions from a central point, usually with a few to several short, divergent branchlets at each branch tip.
At the tip of each branchlet is a hemispheric to round head of 3 to 18 stalkless spikelets (flower clusters). Spikelets are 2 to 8 mm long (to ~1/3 inch), oval to egg-shaped, blunt at the tip, greenish to dark brown, with the florets spirally arranged. Florets are perfect (both male and female parts) each with a 2-parted style (rarely 3-parted) and subtended by a single scale. At the base of the cluster are 3 or more leaf-like bracts, the bract blades shorter than to longer than the cluster branches. Bracts at the base of auxiliary branches are more scale-like.
Leaves and stems:
4 to 11 leaves are alternately arranged along the stem, 9 to 24+ inches long and 5 to 20 mm (to ~¾ inch) wide. Sheaths are strongly to lightly tinged purplish-red at the base and have numerous cross-partitions that may or may not be conspicuous. Stems are single or a few from the base, erect, smooth and 3-sided in cross-section with rounded angles. Plants form colonies from long, spreading rhizomes.
Fruit develops in early to mid-summer, the mature achenes (seeds) dropping off individually and the scales soon after, leaving behind naked branchlets. Scales are 1.1 to 3.4 mm long, generally oval-elliptic, blunt to pointed at the tip with a midrib that may extend not more than .2 mm. Scale color is green to black, the midrib initially green turning light brown. Achenes are .7 to 1.6 mm long, .8 to 1 mm wide, lens-shaped in cross-section, elliptic to urn-shaped in outline, pale brown to creamy colored at maturity. Surrounding the base are 3 to 6 (usually 4) barbed, pale bristles that are slightly shorter to slightly longer than the achene.
Scirpus microcarpus is a species of shores, marshes, swales, ditches and other open wet places mostly in the notheastern quadrant of Minnesota, with scattered populations farther west and south. While traveling through northern Itasca and Cass counties, there was hardly a wet ditch we passed by that didn't have it growing in abundance. It vaguely resembles 4 other Minnesota Scirpus species (Scirpus georgianus, Scirpus hattorianus, Scirpus atrovirens, and Scirpus pallidus) but should not be easily confused with any other bulrush. Scirpus microcarpus is distinguished by its 4 or more stem leaves, purplish-red sheaths, 2-parted styles with lens-shaped achenes (rarely 3-sided), and many-branched clusters with 3 to 18 spikelets in a hemispheric to roundish head at each branch tip. The other 4 listed above have green sheaths, 3-parted styles, 3-sided achenes, and the spikelets tend to be more densely clustered in rounder heads with fewer and stiffer branches. The plants also tend to be taller, averaging about 4 feet where S. microcarpus is more often closer to knee-high.
Compare these with other Bulrush species, which may differ by their round or more sharply 3-sided stems, green sheaths, erect bracts that appear to be a continuation of the stem, less leafy stems, nodding clusters, some or all spikelets single at branch tips, 3-parted styles with 3-sided achenes, or other traits not as above.
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- Scirpus microcarpus plant
- Scirpus microcarpus plants
- Scirpus microcarpus in a wet grassy ditch
- Scirpus microcarpus in shallow water
- Scirpus microcarpus with Scirpus atrocinctus
- stem leaf sheaths are also red at the base
- cross-partitions are conspicuous or not
- scan of spikelet clusters
- more spikelet clusters
Photos by K. Chayka taken in Aitkin and Cook counties. Photos courtesy Peter M. Dziuk taken in Aitkin county.
Have you seen this plant in Minnesota, or have any other comments about it?