Flower:

Branching clusters, taller than wide, 6 to 14 inches long, lance-oval in outline, the main branches spreading to arching, typically nodding over to one side of the stem. Spikelets (flower clusters) are numerous and 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 2.5 to 5mm long (typically less than 4), the upper 4.5 to 7.5mm (typically less 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, 7.5 to 12mm long, the edges rolled in (involute), 3 to 7 veined; the palea is pale, less than half 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, blue-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. The ligule (membrane where the leaf joins the sheath) is .1 to .4mm long with a fringe of short hairs along the top edge. Nodes are green to purplish, with a ring of 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 persists tightly wrapping the stem. Upper stems are green, lower to mid stems are dull green to tan. Stems are ribbed and rough textured, unbranched, erect, and slow to deteriorate, dead stems often persisting through the next season. Dense colonies are formed from both long rhizomes and stolons.

Fruit:

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.

Notes:

Phragmites australis 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); subsp. berlandieri is found in the southern US from California to Florida and into Mexico, subsp. americanus, a.k.a. Phragmites americanus, is widespread in North America, but its national distribution is not altogether clear since the separation of subspecies is a fairly recent thing. The European subspecies was probably introduced by accident in the 18th or 19th century and proved to be quite invasive, displacing the native subspecies in many areas, particularly in the northeast and around the Great Lakes. The US Forest Service provides more information on its origin and how this pest spreads. Even so, it was found to have some value sequestering nutrients and heavy metals and is currently used for this purpose in waste treatment facilities. There was also a proposal some years ago to cultivate it as a biofuel, something environmentalists strongly objected to and for good reason. Management of infested areas is very difficult, since plants can resprout from root fragments, and it produces a much higher amount of viable seed than the native, which is dispersed by wind and water. Subsp. australis is definitely an under-reported species in Minnesota, as we've seen it in a number of road ditches across the state not recorded at EDDMapS.

Older references do not distinguish the subspecies, 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. americanus page for more images and additional information on the native. 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.