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Archive for November 18th, 2009

The shoreline above illustrates a typical set of plants found at the water’s edge. With their feet in the water are clumps of sedges and grasses. At the edge of the shore are cattails. Behind the cattails, on the left, are taller reeds with their fluffy seedheads. To the right, you can see the fall yellow-gold of young larch trees. On dry land, in the distance, is the forest. The reeds are Common Reeds, or Phragmites australis. They are easily recognized in the fall, both by their full, plume-like seedheads and their long stems. Often ten or twelve feet tall, they tower over other plants.

Fossil records show that phragmites have been present in North America for at least 40,000 years. While the term reed is sometimes used generically to indicate tall, grass-like plants, phragmites are the only plant correctly called reeds. They grow in large, dense, colonial clumps and can be found along marshes and wetlands, even ditches. Unlike cattails, which like some water movement, phragmites grow on land or in shallow, still water.

In spite of their conspicuous seedheads, phragmites reproduce predominately via rhizomes and stolons. They send out runners that can extend a long distance, sending up new shoots along their length. The photo above, taken in September, shows phragmites making serious inroads into new territory. Clonal colonies can be very large and extremely long-lived. Phragmites can play a role as land-formers. They divide up shallow water with their network of horizontal runners and vertical shoots. Mud, algae, dead leaves and other debris becomes trapped in the network and slowly, new ground is built up.

Although phragmites are native in North America, something has changed over the last 150 years. Their distribution and abundance has increased dramatically. Botanical records from the 1800s list phragmites as rare or uncommon and phragmites were limited to the southeastern states. By the early 1900s, the plant was more widespread. Now, phragmites are found throughout the United States and into southern Canada.

Scientists investigating possible causes for this change have found molecular evidence that suggests native phragmites are no longer the plants they once were. Phragmites australis is a cosmopolitan plant, found widely around the world. However, different strains are limited to different locations. Molecular studies that have compared modern North American populations with historical ones from herbarium collections indicate that an introduction has occurred. Furthermore, the introduced variety of Phragmites australis has largely displaced the native species. In addition, the non-native phragmites have spread to regions not known to have phragmites present historically.

This is termed a cryptic invasion. The introduced species is so similar to the native species that it is nearly impossible to tell them apart without testing. However, the introduced species doesn’t act like the native species.

Phragmites provide cover, and a few birds, such as black-crowned night herons, may nest in their dense stands. The only mammal that is known to feed on them to any extent is the muskrat. While not problematic in limited concentrations, the continuing expansion of their range and population is a concern as the invaders squeeze out native species that play important roles in wetland ecosystems. You can read more about phragmites as cryptic invaders in Saltonstall’s Cryptic invasion by a non-native genotype of the common reed Phragmites australis, into North America, published in the February 19, 2002 edition of the Proceedings of the National Academy of Sciences (PNAS).

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