Plant of the Week

USDA Plants distribution map for the species.
Eleocharis palustris range map. USDA PLANTS Database.

Eleocharis palustris.
Eleocharis palustris, Willard Bay, Box Elder County, Utah. Photo by Bill Gray.

Eleocharis palustris.
Flowering spikes of Eleocharis palustris. Photo by Max Lichner.

Eleocharis palustris.
Close-up of the flower spike of Eleocharis palustris, Glacier National Park, Montana. Photo by Peter Lesica.

Eleocharis palustris.
Eleocharis palustris in habit. Photo by Max Lichner.

Common Spikerush (Eleocharis palustris)

By Walter Fertig

At first glance, spikerushes (genus Eleocharis) do not look much like flowering plants. Most of the 200 or so species recognized worldwide have only rudimentary leaves (these often appear as bladeless scales tightly pressed against the lower stem) and a small cone or ball-shaped flower cluster at the tip of an unbranched stem. The flowers lack showy petals or sepals and are enclosed by dark brown or black bracts. The whole plant has the appearance of a green matchstick growing in a small clump or in a row, depending on whether a long underground rhizome is present or not. The spikerush is not a plant that is going to win a prize at the county fair or be displayed on a tee-shirt, calendar, or fine painting.

Ecologically, the spikerushes are an important component of wetland habitats, and at least one species is present in riparian areas across the entire continent. Befitting its name, Common spikerush (Eleocharis palustris) is one of the most widespread species, occurring in every state in the union except Florida and Georgia (where other spikerush species take its place), as well as across northern Europe and Asia. It is equally at home in coastal swamps, mountain bogs, and streamsides, as it is along broad rivers, or in desert alkali wetlands. Such a widespread and ecologically plastic species is also quite variable genetically and morphologically. Taxonomists have proposed splitting E. palustris into more than seven different species or numerous subspecies based on differences in the number of chromosomes, overall stature, and technical features of the flowering scales and fruits. Unfortunately, no clear pattern has emerged and many of the purported distinguishing characteristics co-occur within populations or may be environmentally influenced.

The best way to tell different spikerush species apart is to locate the ripe fruits in late summer. Like other members of the sedge family (Cyperaceae), Eleocharis has hardened, nut-like fruits with a single seed called an achene. The top of the achene is crowned by a short tooth or diamond-shaped structure called a tubercle. Differences in tubercle size and shape as well as variation in the color and texture of the main body of the achene can be used to reliably tell one species from another. In the case of Common spikerush, the achenes are smooth and bright golden-yellow with an arrowhead-shaped tubercle on top. These fruits provide a nutritious meal for a wide variety of wetland bird species.

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