NON-NATIVE AQUATIC WEEDS

For inquiries contact Matt Hickler, Biology Department, University of Massachusetts Amherst

What is an invasive non-native species?

Most plants are adept at finding and colonizing suitable habitats. However, the oceans which separate the earth's land masses are formidable barriers to colonization and the floras of isolated regions have evolved with little sharing of species since the breakup of Pangea. It is only in the last few hundred years with the advent of regular intercontinental travel that we have begun introducing plants into North America which surely would not have made it here by natural means. In New England, botanists estimate that 30% of the flora is composed of non-native species; these are plants which can be found growing in the wild without cultivation which have arrived since the first European colonists settled here. The majority of these, like dandelions crabgrass and agricultural weeds rarely become established in natural habitats and, although they may be annoying, are of little concern to biologists. However, some introduced species become invasive. that is, they are able to invade natural communities and compete with native species for space and other limited resources. Often times these species arrive without the diseases and predators which help keep them in check in their native ranges, and as a result introduced populations are unusually vigorous.

To be considered invasive, a species must be adept at colonizing new sites; in-other-words, it must have an effective way of getting seeds or other propagules from established population sites to potential habitats which may be some distance away. In addition, once established, an invasive species spreads aggressively through the new site, competing with native species for space and other resources. Over time, populations of the invasive species increase while native species decline. Ultimately, some native species may become extirpated (locally extinct) at sites which have been invaded.

Some of our most worrisome invasive aquatics can reproduce by fragmentation as well as more conventional means and once established spread by clonal growth. These species, break easily into small pieces, and each fragment is capable of regenerating a whole plant. New sites may be colonized when fragments are transported on floodwaters, migrating wildlife and boats. In a Minnesota study, fragments of aquatic plants were found on 23% of all tailored boats inspected.

In 1997, the Massachusetts Department of Environmental Management Lakes and Ponds Program published a bulletin describing Massachusetts' 13 least wanted non-native aquatic plants. The following species are on the list:

Fanwort, Cabomba caroliniana
Water Chestnut, Trapa natans
Variable watermilfoil, Myriophyllum heterophyllum
Eurasian watermilfoil, Myriophyllum spicatum
Curly-leaved pondweed, Potamogeton crispus
Naiad, Najas guadalupensis
European naiad, Najas minor
South American waterweed, Egeria densa
Yellow floating heart, Nymphoides peltata
Hydrilla, Hydrilla verticillata
European frog-bit, Hydrocharis morsus-ranae
Flowering rush, Butomus umbellatus
Parrot-feather, Myriophyllum aquaticum

Some additional semi-aquatic or wetland species which belong on everyone's list are:

Common buckthorn, Rhamnus frangula
Yellow Iris, Iris pseudacorus
Purple loosetrife, Lythrum salicaria
Phragmites, Phragmites australis

For more information contact:

Massachusetts Department of Environmental Management

Lakes and Ponds Program
(617) 727-3267 Ext. 588

To report an infestation contact:Matt Hickler

For more information, photographs and links try: Center for Aquatic and Invasive Plants