Green Bulrush is a tall perennial herb, growing up to 5 feet high on roundly triangular unbranched smooth upright stems (culms). Not all stems are fertile, non-fertile stems may arch over.
Leaves are 1/3 to almost 1 inch broad (1-2 cm) with a slight "M" shape, smooth on top but rough on the margins. There are 6 to 11 alternate leaves per stem. Veins run parallel with the blade. The leaf sheath can be green in the upper stem or brownish on leaves near the base.
The inflorescence is a compound cyme, terminal and contains several to numerous spherical heads (cymules) containing numerous spikelets, the largest of the cymules will have 17 to 25+ spikelets. Spikelets are stalkless and have dark brown scales. Each scale subtends a flower. These cymules angle out in different directions and under the inflorescence are two or more very conspicuous bracts (modified leaves). These vary in length but one is longer than the inflorescence and their bases are green, sometimes with brown spotting on the blades. The individual cymules may have their own small bracts.
Flowers and Seeds: The individual flowers have 3 stamens, and brownish overlapping scales. The perigynium, common in sedges, is absent. The achenes produced are up to 1.3 mm long and 0.6 mm wide, and when ripe are a brown color with bristles attached. They are spread by the wind. They are very small and need light for germination so should be surface sown. They also need at least 60 days of cold stratification. Sowing in the Fall will take care of that.
Habitat: Green Bulrush is found in sedge meadows, alder thickets and wet meadows. It tolerates standing water. Grows best in full sun, but some shade in hot summer months is good. It grows from rhizomatous fibrous roots that spread and form colonies. Also, as the seeds are viable for up to 40 years, it frequently can colonize a disturbed site such as a site recently dredged or otherwise mitigated. Seeds will self-sow.
Names: The genus Scirpus is the Latin name for the bulrush. The species atrovirens has the base Latin word atro, meaning 'dark' and combined with 'virens' means 'dark green'. The author name for the plant classification, ‘Willd.’ is for Carl Ludwig Willdenow (1765-1812), German botanist, a founder of the study of the geographic distribution of plants. He was director and curator of the Botanic Garden of Berlin.
Comparisons: The bulrush group has many species and there are three close relatives of S. atrovirens in Minnesota that can be confused and occasionally hybridize with it: S. hattorianus, Mosquito or Early Dark Green Bulrush, and S. pallidus, Cloked or Pale Bulrush.
Above and below: Typical dense spherical seed heads (cymules) containing the spikelets. Note the short green bracts that subtend some of the umbels, as opposed to the large bracts at the base of the inflorescence. Drawing of Green Bulrush ©USDA-NRCS PLANTS Database / USDA NRCS. Wetland flora: Field office illustrated guide to plant species.
Below: 1st photo - Young plants emerging in the spring. 2nd & 3rd photos - The development of the inflorescence at the top of the stem above the green bracts. Note that the inflorescence is composed of a number of rounded cymules containing the developing green spikelets.
Below: 1st & 2nd photos - The flowers are surrounded by brown overlapping scales. Spikelets produced are up to 5 mm long, (less than 1/4 inch), with up to 25 per cymule. 3rd photo - The leaf sheath of Dark Green Bulrush is green for upper leaves and light brown on more basal leaves.
Below: 1st photo - Amid the scales of the spikelets you can see the smooth brown color achenes with a bristle attached. 2nd photo - The culm (stem) is roundly triangular in shade with a smooth surface. 3rd photo - The leaf blades are triangular at the point of forming the sheath, then flatten out with one main rib and parallel venation.
Below: 1st photo - The bases of the inflorescence bracts are green, with some brown spotting on the blades. 2nd photo - Leaf sheath.
Notes: Green Bulrush is native to a good part of the U.S., excluding only 7 states in the SW and Florida. It is found in Canada from Manitoba eastward. Within Minnesota, it is found throughout the state with only 14 widely scattered counties not reporting it. It is indigenous to the Garden area.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"