Giant Reed
Arundo donax
Washington State Classification
Monitor List
This plant is on the monitor list, it is not a listed noxious weed in Washington.
Quick Reference
Identification
Growth Habit
Giant reed is a large perennial grass with stems that can resemble bamboo. Plants are mostly glabrous and can grow up to a height of 20 feet or taller. It has well-developed, creeping rhizomes that are typically more than 1 cm thick and often form a dense network.
Leaves
Leaves are alternately arranged, 2-ranked (in one plane), pale green to blue-green in color, 2 to 3.2 inches wide at the base by 11.8 inches to 3.28 feet long. The blades are flat and taper to a fine point, with the middle and base of blade about equal in width. Leaf margins are rough to the touch (scabrous) . Blade bases (region of auricles) light to dark brown, more or less broadly rounded to heart-shaped, clasping the stem, often with long, wavy hairs along the margins.
Flowers
Flowers (florets) are in large, terminal, plume-like panicles. Panicles are open with ascending branches or contracted with more or less erect branches. Spikelets are comprised of 2-4 florets. Floret stalks (rachilla) are glabrous.
Fruit & Seeds
Giant reed fruit is a single-seeded dried fruit (a caryopsis) that is light brown and 3-4 mm long. North American populations are not known to produce viable seeds.
Impact
This plant is on the monitor list, it is not a listed noxious weed in Washington. Please contact Wesley Glisson to report locations or for more information.
Ecology & Spread
Habitat
Giant reed grows in moist places in a variety of soils, from heavy clays to loose sands, but grows best in moist, well-drained soils. It is typically terrestrial but tolerates flooding. Plants establish in riparian areas, floodplains, ditches, culverts, and roadsides. It can often be found along drainage ditches, where it was planted for bank stabilization. Plants tolerate some salinity and extended periods of drought but not in areas with prolonged or regular periods of freezing temperatures. Arundo donax grows in full sun to part shade and can survive in low light levels.
Spread Mechanisms
Reproduction
Giant reed is currently known to spread only by vegetative means in North America, since it does not produce pollen or viable seed. Plants vegetatively reproduce from rhizomes, rhizome and stem fragments, and layering.
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