Sparganium natans (Small Bur-reed)

Plant Info
Also known as: Arctic Bur-reed
Genus:Sparganium
Family:Sparganiaceae (Bur-reed)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; shallow water to 4 feet deep; lakes, ponds, creeks, floating mats, marshes, drainage ditches
Bloom season:July - September
Plant height:4 to 24 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

Flower: Flower shape: indistinct Cluster type: round

[photo of flowering branches] Round flower heads in a spike-like arrangement at the top of the stem, with separate male and female flower heads on the same plant (monoecious). At the tip of the stem is usually a single stalkless male flower head, occasionally 2, covered in dozens of petal-less flowers with yellow-tipped white stamens. Male flower heads turn brown, wither and drop off after pollen release, the naked part of the stem usually persisting for a time but eventually also withering away.

[photo of male and female flower heads] One to 3, well-separated female flower heads sit below the male, are about as large as the males, and are single in the axils of leaf-like bracts, the lowest head often stalked and the upper heads stalkless. Individual flowers have a single style at the tip of a green ovary and are surrounded by scale-like tepals (petals with similar sepals) that lack a darker spot near the tip.

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

[photo of leaves] Leaves are alternate and basal, linear, to 2 feet long, to ¼ inch (2 to 6 mm) wide, rarely wider, hairless, toothless, flat, thin, mostly limp and floating on the surface, the upper stem leaves or leaves on land-locked plants may be more stiff and erect to ascending.

[photo of veins on leaf lower surface] Surfaces are green, the lower surface with green parallel veins and no keel. Leaves become more translucent below the water's surface. Stems are erect, green and smooth. Flowering stems rise slightly above the surface of the water.

Fruit: Fruit type: seed without plume

[photo of developing fruit] Female flower heads form densely packed seed heads that expand up to about ½ inch (12 mm) diameter, the plump, spiky head maturing from light green to dark greenish or brownish.

[photo of fruit] Fruit is oval-elliptic to somewhat inverted pyramidal, the body 2 to 4 mm (to ~1/6 inch) long, tapering at the base, the tip more abruptly tapering to a slender beak shorter than the body and becoming slightly curved at maturity.

Notes:

Small Bur-reed, known as Sparganium minimum in older references, is a circumpolar species native to northern North America, Europe and Asia, and is occasional to common in northern Minnesota. It is found in the quiet, shallow waters of lakes, ponds, pools in marshes and swamps, and slow-moving creeks and drainage ditches, usually in less than 2 feet of water, occasionally deeper, and sometimes becoming land-locked when water recedes.

There are 4 Sparganium species in Minnesota that have long, ribbon-like floating leaves; S. natans is the smallest Sparganium in the state, distinguished by stems under 2 feet long, widest leaves 3 to 6 mm wide, unbranched flower clusters, usually a single male flower head at the tip of the stem (occasionally 2), 1 to 3 female heads stalkless or the lowest head stalked, fruiting heads up to ½ inch (12mm) diameter, fruit with short, tapered beaks that often become slightly curved with maturity. It can form colonies that may have few flowering stems.

Of the Sparganium species with floating leaves, all the others usually have 2 or more male flower heads or branched flower clusters. Narrow-leaf Bur-reed (Sparganium angustifolium) is most similar, may grow to 6+ feet long, usually with 2 to 4 male heads crowded at the tip and appearing as a single elongated head, female heads stalkless or on a stalk that is at least partly fused to the stem (supra-auxillary). Floating Bur-reed (S. fluctuans) has widest leaves 6 to 10 mm, branched flower clusters, and fruit is distinctly red with strongly curved beaks. Unbranched Bur-reed (Sparganium emersum) sometimes has floating leaves but more often has stiffer, erect leaves that are keeled on the back and triangular in cross-section. American Eelgrass (Vallisneria americana) also has long, ribbon-like leaves, but with a very different vein pattern.

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More photos

Photos by K. Chayka taken in Wisconsin. Photos by Peter M. Dziuk taken in Cass, Cook and Lake counties, and in Wisconsin. Photos by Steve Eggers taken in Wisconsin.

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