Dear Friends of Maine Lakes, Thank you for visiting our Interactive Field Guide! Though the primary content pertaining to species identification in this Guide is—for the most part—still correct and useful, the site itself is no longer fully-functional (nor able to be updated). The entire Guide will soon be replaced by a new, expanded website-version of the Maine Field Guide to Aquatic Phenomena. So please stay tuned! Thank you for your patience!

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The primary purpose of the Virtual Field Guide is to help users recognize the eleven invasive aquatic plants on Maines invasive aquatic plant list, and to distinguish these invaders from their more common native look alikes. One does not need to have previous knowledge of aquatic plants to use the Virtual Herbarium, or, for that matter, to successfully detect a suspicious aquatic plant. Indeed, most of the aquatic plant infestations known to date in Maine have been detected by those with limited experience in plant identification.

Though familiarity with the native plants is not a prerequisite for successfully screening waterbodies for invasive plants, it does provide some advantages. The more familiar one becomes with the plants that belong in a particular waterbody, the greater the likelihood that one will notice an outsider if and when it does appear. It is not unusual for ones familiarity with Maines native aquatic plants to increase naturally during the survey process. This guide offers a starting point in this regard, providing useful information regarding some of the more common native plant species found in Maine waters.

Generally, only common native plants that share one or more notable characteristics with one of the eleven listed invaders are included in the Virtual Herbarium. Less common species have been included only in cases where the rarer species is a very close look alike to one of the listed invaders. Recommendations for additional native plant identification resources are provided in the Sources section.

For those with some familiarity with aquatic plants, many of the more common plant species can be easily ruled out as being suspicious by observing them from a boat, using a viewing scope as needed. However, when one is starting out in unfamiliar territory, it is a good idea to plan on collecting representative specimens from suspicious or unknown plants for later, more-detailed observation. For some plant species, accurate identification is virtually impossible (even for the seasoned expert) without collecting specimens for closer scrutiny.


1. Read through the material on plant structure. If you have recently participated in Invasive Plant Patrol (or equivalent) training, a quick review of this section should be sufficient.

2. Use the simplified Plant Identification Key provided to determine a possible identification for the plant in question. Click on the links to take you to the page(s) indicated, and compare your specimen to the featured plant(s). Also check your specimen against all of the look alike plants listed for each featured species. Plant names shown in colored fonts, where used, indicate native or invasive status: red indicates an invasive plant species and green indicates native plant species.

CAUTION: Even after one has ruled out all eleven invaders on Maines invasive aquatic plant list, it still pays to be cautious. New invasive plants (plants that are not yet officially listed in Maine) may be introduced to our region at any time. If you notice a plant that seems to be spreading unusually fast, and you cannot identify it, please collect a specimen, and send it to VLMP for identification, as described below. For more information on non-listed invaders, please see Other Invaders on Maines Radar Screen.

3. Specimen collection should be done with great care. Select specimens for collection that are in relatively good condition (no major deterioration or insect damage), including any flowering or fruiting structures, winter buds, distinctly different leaf-types, or other features that may help with the identification. For floating-leaf plants, collect one or two floating leaves and a portion of the leaf stem, including any submersed leaves that may be present. For submersed plants, collect three or four small stem fragments (15 to 20 cm long), including the growing tips. For the diminutive bottom dwellers, select one or two individual stems or rosettes from the colony.

When collecting specimens, it is important to ensure that ones activity will not adversely impact the local plant populations. This is true whether the plants in question are suspicious of being invasive, or not. Native plant communities perform many functions that are vital to the ecosystem, and sometimes include rare or endangered species. For these, and many other reasons, native plants warrant our respect and protection.

But care must also be given when encountering invasive plants. Most invasive aquatic plants are easily spread by tiny plant fragments. Every effort must be made to minimize disturbance of such plants. Once an invasive species has been verified and the Maine Department of Environmental Protection has been notified a permit will be issued. The plants can then be carefully removed by those who have been properly trained to carry out such activity.

Plant specimens may be spread out in a tray of water (a white or light-colored tray works best) and observed. A good 5X to 10X hand lens is helpful for observing minute features. If multiple specimens are being collected, individual specimens may be placed (with enough water to float) in labeled zip-lock bags and stored in a cooler for later observation.

If you think you have found an invasive plant, mark the location of the plant with a weighted buoy and carefully collect a specimen for species confirmation. Place the specimen in a sealed container of water and store in a cool place. Alert the Volunteer Lake Monitoring Program at 207-783-7733 or immediately. You will be given directions for shipping the specimen. Also, see If You Find a Suspicious Plant.


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Maine Volunteer Lake Monitoring Program
24 Maple Hill Road, Auburn, ME 04210

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