Morphological differences between
The recent development of molecular markers identifying native and non-native populations of Phragmites in North America now makes it possible to look for morphological characters potentially distinguishing these lineages. Preliminary observations of populations in New York (Fig. 1), Maryland, Maine, Indiana, Wisconsin, Minnesota, Virginia, Arizona, Washington, and Louisiana as well as examination of numerous herbarium specimens indicate that such morphological differences may exist (Table 1). [Please note: We are updating Table 1 as new evidence emerges. Please check frequently or sign up for our email list so you are automatically informed if updates are provided. In the most recent update, various traits were deleted (node coloration, ligule color, stem straightness) because they did not provide consistent separation of native and introduced haplotypes. Others were added (rhizome diameter and color, leaf sheath characters, habitat requirements) ].
Please note that these traits are based on examination of now a considerable number of native and introduced clones but need further confirmation. What has become particularly clear over the past few months is that the various North American haplotypes differ in their morphological characters. And that these characters change over the course of the season and through the winter. Please also remember that the specimens you see in the field are the result of the genotype and its interactions with the biotic and abiotic environment. The same genotype grown in the moister Northeast will look quite different in the arid West. We are further examining these differences through field visits and by creating an experimental garden in Ithaca where different haplotypes are grown under standardized conditions. We need your help to identify and map other growing locations of native genotypes. We also need to increase the sample size to assess whether the preliminary evidence for morphological differences between native and introduced genotypes is consistent across populations and lineages. By the end of May we will offer a diagnostic service using the identified morphological characters for those that need or want to know whether their local Phragmites patch is native or introduced.
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Table 1. Observed differences between native and introduced Phragmites clone
In general, native populations appear to have a lower stem density, and produce a reddish-purple color on their stems and ligules in spring and summer that is not present in non-native populations. When checking for these differences note that the side of the stems exposed to the sun will show the brightest coloration. The reddish color fades somewhat into a chestnut brown in the fall but was still very obvious in October in Virginia; in the winter the red stems turn light to chestnut brown and somewhat gray. Stems of native genotypes are smooth and shiny as if polished, particularly in the winter, while stems of introduced genotypes are dull, rough and ribbed (ridges visible with the naked eye once leaf sheath has been removed). These differences are easy to recognize by running your fingers up and down them stems.
Please note that a leaf sheath wraps around the stem almost entirely. It is important to remove the leaf sheath when checking for stem morphology or texture.
For all native genotypes leaf sheaths either fall off by themselves or are very easily removed when handling Phragmites. In the introduced genotypes, leaf sheaths may fall off at the base of the stem (which is also occasionally reddish or brownish) but on upper nodes are very difficult to remove (hold a stem close to an internode and use a twisting motion to check). In instances where native and introduced clones grow in close vicinity of each other, differences in stem density and stem toughness become obvious on windy days. Introduced genotypes remain sturdy and erect and move little while native genotypes easily bend and swing in the wind. Stems of introduced genotypes are often almost perfectly straight while stems of native genotypes often grow crooked (Haplotype E, known from the Northeast and Midwest does conform to this pattern but not all other populations).
In the fall and winter, differences in the density of inflorescences are also obvious; introduced genotypes appear to have much denser and larger inflorescences. Observations in New York and Virginia also suggest that native genotypes senesce earlier than introduced genotypes (this is a common phenomenon in introduced species which often show extended growing periods). In addition, an unidentified stem fungus attacks native genotypes with dark spots often clustered around internodes while introduced genotypes remain fungus free (there appears to be a reduction over the winter in the abundance of this stem spot fungus and not all western populations appear to be attacked).
Excavations of rhizomes at several sites have also produced consistent differences between native an dintroduced haplotypes. Native haplotypes have round rhizomes that are yellow and rhizome diameters of less than 15mm. Rhizomes of introduced haplotypes, particularly when freshly excavated and rinsed are white (they darken over time) and compressed (flattened). Although there are some rhizomes with diameters <15mm, most rhizome diameters in introduced genotypes are larger than 15mm (measure in the center of an internode and use largest diameter).