Flower:

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); occasionally a short branch arises from the uppermost leaf axil. At the tip of the stem are 3 to 8 stalkless male flower heads, most not tightly crowded, each 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.

One to 6 female flower heads sit below the males, are slightly larger than the males, and are single in the axils of leaf-like bracts, the upper head(s) typically stalkless, the lowest head(s) usually stalked with the stalk at least partially fused to the stem so the head looks attached to the stem above the axil (known as supra-auxillary); any female heads on a branch are 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).

Leaves and stems:

Leaves are alternate and basal, mostly erect to ascending, linear, to 30 inches long, to ½ inch (4 to 12 mm) wide, hairless, toothless, flat on the upper surface, keeled on the back and triangular in cross section at least towards the base.

In deeper water ribbon-like floating leaves may be produced, which are limper than emersed leaves, to 6 feet long, 4 to 18 mm (to ~¾ inch) wide. Stems are erect, green and smooth. Flowering stems rise above the surface of the water and are much surpassed by the leaves.

Fruit:

Female flower heads form densely packed seed heads that expand up to about 1 1/3 inch (to 35 mm) diameter, the plump, spiky head maturing from light green to reddish-brown.

Mature fruit is shiny, the somewhat fiddle-shaped body 3 to 4 mm (to 1/6 inch) long, constricted at or just below the middle, tapering to a stalk-like base (stipe), the tip abruptly tapering to a slender, straight beak more or less as long as the body.

Notes:

Unbranched Bur-reed is a common aquatic especially north of the Twin Cities, found in the quiet waters of clear lakes, ponds and slow-moving rivers, usually in less than 2 feet of water, occasionally deeper, and can become stranded on shores when water recedes. Leaves are most often erect to ascending but can become floating in deeper water or sometimes in flowing water. Where we found floating leaves the plants were anchored in knee-deep muck with water about waist high.

Of the Sparganium species with erect leaves, S. emersum is distinguished by the usually unbranched flower clusters (occasionally 1 branch), at least some supra-auxillary female heads, and mature fruit that is shiny, constricted near the middle, and has a straight beak more or less as long as the body. Of those species with long, ribbon-like floating leaves, S. emersum is further distinguished by widest leaves 6 to 18 mm wide that are keeled and triangular in cross-section at least near the base.