Ecology: Glyceria maxima is typically found in open wetlands such as marshes, meadows, shrub-carrs and along shorelines (Campbell et al. 2010, King County 2012). It performs better in waterlogged soils that have direct sunlight, but can be found in partially shaded areas adjacent to woodlands as well (Forest Health Staff 2006, van der Putten et al. 1997).
Glyceria maxima can expand into shallow water (~ 30 cm) and survive prolonged flooding because of its aerenchyma tissue and superficial root system (Lawniczak et al. 2010, Studer-Ehrensberger et al. 1993). The root system and rhizomes can extend 3 feet down into the soil (King County 2012). When growing near open water, reed mannagrass can form floating mats attached to the shore (King County 2012).
This species primarily reproduces vegetatively via rhizomes in North America (Campbell et al. 2010, Forest Health Staff 2006). Reed mannagrass emerges early in the year and concentrates up to 50% of its biomass in its root system (Westlake 1966). The energy stored in the roots and rhizomes enable this species to produce new shoots through the growing season (Buttery and Lambert 1965). Muskrats and beavers may aid the expansion of G. maxima. While foraging, plants may become uprooted and portions of the rhizomes may break off, float down stream, and re-establish (Forest Health Staff 2006).
Glyceria maxima also has florets that can bloom and produce viable seed (IPANE 2004). Individuals are in bloom between June and August. Once the inflorescences are mature, the panicle opens and rises above the other foliage (Campbell et al. 2010, Forest Health Staff 2006). The dark brown seeds are 1.5-2 mm in length, egg-shaped, and smooth except for a deep, slender furrow down the middle (IPANE 2004). Seeds dispersed in the fall will likely germinate the following spring; however, seeds can remain dormant and viable in the soil for several years (King County 2012).
During the winter, reed mannagrass becomes dormant. In early spring, regrowth occurs from rhizomes buds (King County 2012).
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This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.