Cyperus subsquarrosus (Dwarf Bulrush)
|Also known as:||Small-flowered Hemicarpha, Small-flower Halfchaff Sedge|
|Habitat:||part shade, sun; sandy or mucky shores and river banks|
|Fruiting season:||July - October|
|Plant height:||1 to 6 inches|
|Wetland Indicator Status:||GP: FACW MW: OBL NCNE: OBL|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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One to 3 stalkless spikelets at the top of the stem, subtended by 1 to 3 bracts ¾ to 2 inches long, the longest of which is usually erect, appearing to be a continuation of the stem so spikelets seem to be growing out from the side of the stem. Secondary bracts, if present, are angled away from the spikelets.
Spikelets are 2 to 5 mm (less than ¼ inch) long, egg-shaped to round, rounded at the tip, with 30 or more florets spirally arranged. Florets are perfect (both male and female parts) each with 1 stamen, a 2-parted style and subtended by 1 or 2 scales. The primary scale is 1 to 3 mm long, abruptly tapered to an extended tip, initially whitish with a green midrib, turning orange-brown with age; the secondary scale is less than a quarter as long but is usually absent altogether.
Leaves and stems:
Leaves are basal, some of which are reduced to bladeless sheaths, the rest shorter than the stems, sometimes flat or more often rolled in along the edges and resembling the stems. Stems are round in cross-section, erect, arching or prostrate from the base, and multiple from the base usually forming dense clumps.
Fruit develops summer into fall, the mature achenes (seeds) dropping off individually. Achenes are about .5 mm long, generally narrowly elliptic, widest at or above the middle, round in cross-section, gray to brown, the surface covered in tiny pits. Bristles around the base are absent.
Cyperus subsquarrosus was formerly known as Lipocarpha micrantha, and Hemicarpha micrantha before that. It's found primarily on sandy or mucky shores after water levels have receded in mid to late summer. In Minnesota it's most often seen along the Mississippi River on mucky banks and exposed sand bars, as well as sandy lake shores.
It bears some resemblance to another small, clump-forming bulrush, Schoenoplectiella smithii, which has larger spikelets, 5 to 10 mm long, that are more pointed at the tip and fewer flowered, and has broader achenes that are flat on one side and usually have 4 to 6 bristles around the base. Cyperus hemidrummondii, formerly Lipocarpha drummondii, not known to be in Minnesota but recorded in neighboring states, is also very similar but consistently has 2 scales on flowers, the secondary scale nearly as long as the primary.
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Photos by K. Chayka taken in the backwaters of the Mississippi River, Dakota County. Photos by Peter M. Dziuk taken in Dakota County and in Wisconsin.
Have you seen this plant in Minnesota, or have any other comments about it?