Sparganium eurycarpum (Giant Bur-reed)

Plant Info
Also known as: Broad-fruit Bur-reed
Genus:Sparganium
Family:Sparganiaceae (Bur-reed)
Life cycle:perennial
Origin:native
Habitat:sun; shallow water; lakes, streams, river banks, floating mats, swamps, marshes, swales, wet ditches
Bloom season:June - August
Plant height:2 to 6 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

Pick an image for a larger view. See the glossary for icon descriptions.

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 and on branches arising from the axils of leaf-like bracts on the upper stem, with separate male and female flower heads on the same plant (monoecious).

[photo of male flower heads] Up to 12 male flower heads are at the tip of the stem or branch, crowded or not, each head stalkless and covered in dozens of petal-less flowers with yellow-tipped white stamens. The male flower heads open from the bottom of the spike up, turn brown, wither and drop off after pollen release, the naked part of the stem or branch usually persisting.

[photo of female flower head] Female flower heads sit below the males and are larger than the males, with (0)1 or 2(6) stalkless flower heads per branch and those on the main stem more commonly stalked. Individual flowers usually have a 2-parted style and are surrounded by greenish to brown, scale-like tepals (petals with similar sepals) that have a darker spot near the tip.

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

[photo of leaf front and back] Leaves are alternate and basal, erect to ascending, linear, to 5 feet long, ¼ to ¾+ inch (to 20 mm) wide, hairless, toothless, keeled on the back and triangular in cross-section, though may be flat towards the tip. Stems are erect, stout, green and smooth. Flowering stems rise well above the surface of the water but do not typically rise above the leaves.

Fruit: Fruit type: seed without plume

[photo of fruiting heads] Female flower heads form densely packed seed heads that expand up to 2 inches diameter, the plump, spiky head maturing from green to brown.

[photo of fruit] Fruit is inverted pyramidal in shape, the body up to 10 mm (3/8 inch) long, half to nearly as wide, somewhat rounded at the tip and abruptly tapering to a straight beak 3 to 4 mm long, less than half as long as the body.

Notes:

Giant Bur-reed is the most common Sparganium species in Minnesota, a robust plant found in lakes, rivers and wetlands across the state. It is also one of the more easily identified as the only species with 2-parted styles on the female flowers. Most, if not all, flowers have this trait and the styles often persist while fruit develops. The fruit is also unique with its pyramidal shape and proportionately short beak. All other Sparganiums have single, undivided styles, more elliptic fruit and the larger species that otherwise may resemble it tend to have proportionately longer beaks on their fruit.

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More photos

Photos by Peter M. Dziuk taken in Aitkin, Big Stone, Cass, Clay, Cook, Lake, Redwood and Winona counties.

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