Phragmites australis ssp. americanus   American reed
           (Alt: Phragmites communis )
Poaceae (Alt: Gramineae )
native                      grasslike           east Foothills

UW Burke Herbarium Link: Phragmites australis ssp. americanus

Common reed (Phragmites australis) is extremely widespread in temperate and tropical areas throughout the world, but it is only occasionally encountered in the Boise Front region.  It is most easily seen at Hyatt Hidden Lakes Reserve, where it forms patches at the edge of the more abundant cattails.  It is also established at some mid-slope seepage areas in the foothills, including the conspicuous one opposite the Freestone Creek trailhead in Military Reserve.

The species used to be known as Phragmites communis, until it was determined that P. australis had priority and was therefore the correct name according to nomenclatural rules.  It is now also understood to consist of several subspecies, with both native and non-native subspecies present in North America (e.g., Saltonstall et al., 2002, 2004).  As a further complication, the non-native subspecies (ssp. australis) is invasive, but morphologically can be told apart from the non-invasive native subspecies only by relatively subtle characters. The majority of historical collections and reports have not been identified to subspecies, although some are sometimes mistakenly defaulted to ssp. australis.  My current, still tentative, conclusion is that only the native ssp. americanus is present in the Boise Front area, in part because it is not behaving as an invasive newcomer.  However, more work is needed to confirm this, since distinguishing measurements are often in the overlap zone and access to confirmed comparative material is limited.

Key morphological differences between the subspecies (based on FNA and Flora of the Pacific NW):

native ssp. americanus:  Lemmas 9.3–9.9 mm long; lower glumes 2.8–7 mm long; upper glumes 5.5–11 mm long; membranous portion of ligules on middle leaves 0.2–0.9 mm long; leaf sheaths remaining attached and covering stems in winterz, lower internodes red to purple, smooth and shiny late in the growing season.

invasive ssp. australis:  Lemmas 6.4–8.7 mm long; lower glumes 2.5–4.8 mm long; upper glumes 4.5–7.5 mm long; membranous portion of ligules on middle leaves 0.1–0.4 mm long; leaf sheaths detaching and exposing stems in winter, lower internodes yellow to yellow-brown, ridged and not shiny late in the growing season.

A third subspecies, ssp.  berlandieri, occurs primarily to south of us but could also be potentially present.  It most resembles ssp. australis but has smooth shiny internodes.

Saltonstall, K.  2002.  Cryptic invasion by a non-native genotype of the common reed, Phragmites australis, into North America.  Proc. Natl. Acad. U.S.A. 99:2445–2449.

Saltonstall, K., P.M. Peterson, & R.J. Soreng.  2004.  Recognition of Phragmites australis  subsp. americanus (Poaceae: Arundinoideae) in North America: evidence from morphological and genetic analysis.  Sida 2(2):683–692.

 

 

Walks that mention Phragmites australis ssp. americanus