Sparganium identification key and species descriptions


By Josh Sulman

University of Wisconsin-Madison

Department of Botany

Updated March, 2016


Text Box: Fig. 1 Sparganium androcladum from Taylor County, WI, Aug 2008. Showing, from top: 5 mature male heads; 4 mature female heads, the lower 2 axillary; 2 lateral branches bearing immature male heads.Sparganium research homepage

Sparganium Photo Gallery

Key to species


SIdentifying bur-reeds in the field presents a special challenge to botanists, wetland scientists, and anyone interested in aquatic plants. The group has its own set of specialized terms. Often, at least until mid-summer, it is necessary to be familiar with vegetative characteristics of the different species. Most fruits are not ripe until late summer, so understanding the features of the flowers and inflorescences is important for spring or summer field surveys. Additionally, there is remarkable phenotypic plasticity within species. Plants of some species are typically limp and floating, but erect and emergent during periods of low water levels. Also, typically erect and emergent species are occasionally found limp and floating in deep water or flood conditions.



The treatment of Sparganium by Robert Kaul in the Flora of North America (1997) is a thorough and reliable guide to the genus.

The worldwide monograph (Cook and Nicholls, 1986, 1987) is the most comprehensive taxonomic treatment, and is now available online:

Part 1: Subgenus Xanthosparganium

Part 2: Subgenus Sparganium


A key is presented below to the 8 species found in Wisconsin. Detailed descriptions of the plants will follow.




Text Box: Figure 1:  Sparganium androcladum; inflorescence with 2 branches bearing immature male heads only; main axis with 4 female heads, mature male heads above


General description and ID tips:

The flowers are borne in globose heads, the female flowers borne in separate heads from the male flowers. The male heads are borne at the tips of the inflorescence axis and branches, and the whole male head is deciduous. After it has fallen, you can tell where it was attached by the scar that is left on the stem.  A branch bears 2 or more heads; a “branch” bearing a single head is a peduncle.


The female flowers are packed into spiky heads of their own. Each female flower will bear one or two stigmas, depending on the species. The stigma remains prominent in fruit, developing into a sharp-pointed beak. The beak may be straight, curved or hooked and may function in dispersing the fruits. The bur refers to the spiky appearance of the fruit heads.