Phragmites australis subsp. americanus (American Common Reed)
|Also known as:|
|Habitat:||sun; moist to wet soil; marshes, swamps, fens, sedge meadows, shores, swales, wet ditches|
|Fruiting season:||September - October|
|Plant height:||3 to 7 feet|
|Wetland Indicator Status:||GP: FACW MW: FACW NCNE: FACW|
|MN county distribution (click map to enlarge):|
|National distribution (click map to enlarge):|
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Branching clusters, taller than wide, 6 to 14 inches long, lance-oval in outline, the main branches spreading to arching, sometimes nodding over to one side of the stem particularly as they dry. Spikelets (flower clusters) are single at the ends of slender stalks that are appressed to slightly spreading from the branch. Spikelets are purplish when young, somewhat flattened, with 3 to 11 florets. The stalk between florets (rachilla) is densely covered in silky white hairs up to 1cm long.
At the base of a spikelet is a pair of bracts (glumes) that are narrowly lance-shaped with a long taper to a pointed tip, 1-veined, the lower glume 3 to 7mm long (typically more than 4), the upper 5.5 to 11mm (typically more than 6). Surrounding a floret is a pair of bracts (lemma and palea), the lemma narrowly lance-linear with a long taper to a pointed tip but not awned, 8 to 13.5mm long, the edges rolled in (involute), 3 to 7 veined; the palea is pale, half or less as long as the lemma and blunt at the tip.
Leaves and stems:
Leaves are alternate, 8 to 24 inches long, 1/3 to 1½ inches (8 to 40mm) wide, green to yellowish-green, flat, hairless and mostly smooth on both surfaces, with a long taper to a pointed tip. Sheaths are smooth, the edges overlapping near the tip or not, and sometimes have short hairs along the edge. The ligule (membrane where the leaf joins the sheath) is .4 to 1mm long with a fringe of hairs along the top edge, the hairs occasionally long but usually short; ligules are somewhat fragile and often shred before long. Nodes are green to purplish, smooth or with a few fine hairs along the upper edge.
Leaves drop off at the ligule at maturity (lower leaves in particular), leaving the sheath, which dries to tan and becomes loose around the stem, often falling off altogether at the node. Upper stems are green, lower to mid stems are somewhat shiny and maroon to reddish brown, though the color may fade in winter. Stems are smooth, unbranched, mostly erect, and typically form small, loose colonies from long rhizomes, though denser colonies may occur.
Florets dry to tan and drop away when mature, leaving the glumes behind persisting on the stalk with the lowest part of the hairy rachilla, giving the remaining seed head a feathery look. The head persists into winter. Grains (seeds) are 2 to 3 mm long but rarely mature.
Phragmites australis is a wetland grass with a feathery plume at the tip of a tall, leafy stem, and is one of the most widely distributed flowering plants in the world. It currently has 3 recognized subspecies: one European (subsp. australis) and two North American (subsps. americanus and berlandieri), though there is talk of raising subsp. americanus to species rank, Phragmites americanus, already accepted in some circles. Subsp. berlandieri is found in the southern US from California to Florida and into Mexico. Subsp. americanus is widespread in North America, but its national distribution is not altogether clear since the separation of subspecies is more or less a recent thing. Most of the records in the Bell Herbarium have no subspecies designation but are assumed to be the native, the older records in particular. The European subspecies was probably introduced by accident in the 18th or 19th century; it is quite invasive and has spread across the continent. Older references do not distinguish them, but there are a number of key differences now known between subsp. australis and americanus:
- americanus does not normally form dense monocultures where australis does, spreading rapidly from hardy rhizomes as well as stolons, which can grow up to 50 feet long and more than 4 inches a day
- americanus is less robust than australis, which is more densely flowered and has tougher stems that do not deteriorate very rapidly, a stand becoming a dense mix of old and new stems
- americanus height does not generally exceed 7 feet, where australis may reach 15 feet or more
- americanus leaves are green to yellowish-green, australis are blue-green, though this isn't necessarily obvious unless they are side by side
- americanus ligules are .4 to 1+mm long (excluding the fringe of hairs), australis ligules are .1 to .4mm long (excluding hairs)
- americanus sheaths are loose and often fall off especially on the lower and mid stem, australis sheaths are tight around the stem and persist. Note that fresh sheaths on americanus can also be tight but loosen as they dry.
- americanus lower to mid stems are smooth, somewhat shiny and maroon to chestnut colored, australis stems are ribbed and roughish, dull green to tan
- americanus glumes are longer than australis, the lower mostly more than 4mm long and the upper more than 6mm, where australis lower glume is mostly less than 4mm and upper less than 6mm
See photos below for comparisons of most of these traits, and the subsp. australis page for more images and additional information on this invasive pest. In either case, Phragmites australis is not likely to be confused with other grasses in Minnesota—it is the tallest grass in the state, though there are other tall grasses with feathery plumes in the nursery trade, such as Pampas Grass and Giant Miscanthus, but have not naturalized here.
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- American Common Reed plants
- American Common Reed plants
- American Common Reed on a sandy beach
- late season American Common Reed
- seed heads persist through winter
- flowering branch
- comparison of American and European Phragmites plants
- comparison of American and European Phragmites glumes
- comparison of American and European Phragmites ligules
- comparison of American and European Phragmites lower stems
- comparison of American and European Phragmites leaves
Photos by K. Chayka taken in Anoka, Chisago, Mahnomen and Polk counties and in North Dakota. Photos courtesy Peter M. Dziuk taken at various locations across Minnesota and in North Dakota.
Have you seen this plant in Minnesota, or have any other comments about it?
on: 2020-10-15 13:48:24
Do you know how aggressive the native subspecies can be? I believe we have a pretty large stand of it on a new property on Lake Virginia in Excelsior, and would like to select adjacent plants accordingly.
on: 2020-10-15 14:11:57
Briana, while the native reed can form fairly large colonies, it plays with its neighbors much better than the invasive non-native.