Scirpus pallidus (Pale Bulrush)

Plant Info
Also known as: Pale Bulsedge
Genus:Scirpus
Family:Cyperaceae (Sedge)
Life cycle:perennial
Origin:native
Habitat:sun; wet; lakes, ponds, sloughs, wet ditches, wet fields, marshes, swamps
Fruiting season:July - September
Plant height:3 to 5 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: round Cluster type: spike

[photo of spikelet clusters] Stiff, open or compact branching cluster at the top of the stem, occasionally also arising from the uppermost leaf axil, the main branches up to 4 inches long and more or less radiating in all directions from a central point, usually with short, divergent branchlets at each branch tip.

[close-up of spikelet head] At the tip of each branchlet is a hemispheric to round head of 12 to 130 stalkless spikelets (flower clusters). Spikelets are 4 to 5(8) mm (to ~¼ inch) long, oval to egg-shaped, blunt at the tip, dark brown though may be more olive green when young. Florets are spirally arranged, perfect (both male and female parts) each with a 3-parted style and subtended by a single scale. At the base of the cluster are 3 or more leaf-like bracts, green at the base though may be brown along the edge. Bract blades are shorter than to longer than the cluster branches. Bracts at the base of auxiliary branches are more scale-like.

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

5 to 10 leaves are alternately arranged along the stem, 8 to 22 inches long and 8 to 16 mm (to ~2/3 inch) wide. Lower leaf sheaths are green to whitish with many 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 loose clumps from short rhizomes.

Fruit: Fruit type: seed without plume

[photo of spikelet, scales and achenes] 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 1.6 to 2.8 mm long, elliptic to egg-shaped with a midrib that often extends to an awn .4 to .7(1.2) mm long. Scale color is variable: greenish when young turning blackish at maturity, the midrib initially green turning light brown. Achenes are .8 to 1.2 mm long, .4 to .6 mm wide, plumply to weakly 3-sided in cross-section, elliptic to urn-shaped in outline, pale brown to creamy colored to nearly white at maturity. Surrounding the base are 5 or 6 barbed, pale bristles that are slightly shorter to slightly longer than the achene.

Notes:

Scirpus pallidus is a fairly common species of shores, marshes, swales, ditches and other open wet places, particularly in the western third and south-central counties of Minnesota. It closely resembles 4 other Minnesota Scirpus species: Scirpus georgianus, Scirpus hattorianus, Scirpus microcarpus, and Scirpus atrovirens. These share the common traits of a weakly 3-sided stem, 3 or more stem leaves, 3 or more leaf-like bracts that are shorter than to longer than the cluster branches, and a terminal cluster with fairly stiff erect to spreading branches that end in dense, hemispheric to round heads of several to many spikelets.

Scirpus pallidus is distinguished by floral scales blackish at maturity with an awn at least .4mm long, 3-parted styles, usually 6 bristles more or less about as long as the achene, cross-partitions that may or may not be conspicuous, and no bulblets in cluster branches. It has the largest spikelet heads, scales and achenes of this group though there is overlap with other species, and it lacks bulblets in the cluster branches, which some others may have and reveal themselves when they sprout late in the season.

The most readily distinguished of this group is S. microcarpus, which is rarely taller than 2 or 3 feet, has purplish-red sheaths, 2-parted styles, and at most 18 spikelets in a head. The other 3 can be very difficult to distinguish from each other and it may be necessary to examine several plants in a population to get a consensus on some traits. S. georgianus, which has only been recorded twice in Minnesota and not since 1983 (probably now extirpated), has at most 3 bristles all shorter than the achene. S. hattorianus is generally a more slender, spindlier plant with longer branchlets but smaller heads, smaller floral scales that are merely pointed at the tip or the midrib extending not more than .2mm, 4 to 6 bristles all shorter than the achene, and may have bulblets on cluster branches. S. atrovirens has somewhat smaller heads, has consistently conspicuous cross-partitions (very noticeable on basal sheaths), slightly smaller floral scales with an awn not more than .4mm long, and often has bulblets on cluster branches. Most references put some reliance on scale and achene colors, but I have found these too subjective and not consistently distinct. Scales on all can be streaked with black and mature achenes can all be creamy colored. And hybrids exist which complicates matters.

Compare these with other Bulrush species, which may differ by their round or sharply 3-sided stems, erect bracts that appear to be a continuation of the stem, less leafy stems, nodding clusters, some or all spikelets single at branch tips, or other traits not as above.

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More photos

Photos by K. Chayka taken in Becker, Pope, Stearns and Todd counties. Photos courtesy Peter M. Dziuk taken in Polk, Pope and Todd counties.

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