Aquatic Plants - invasive

Floating Marsh-Pennywort (Hydrocotyle ranunculoides) on Sep 23, 2013

Submitter does not have a specimen
EDRR Status: Population assessed

Description of specimen

When I first saw it, it reminds me of a four leaf clover that floats on the surface. Just below the green petals are multiple fibrous roots that shoot out and a single root that connects to the next "four leaf clover" petal. I apologize that I didn't take a close up photo. I will do that tomorrow and send it in.

Commentary

Ms. Roth, Thank you for reporting this plant. Over the last week, I've been discussing what action to take on this site with folks from Portland Environmental Services. The plant is an aquatic plant called floating marsh pennywort (scientific name: Hydrocotyle ranunculoides), but it's a rather interesting situation since it’s a native species here in the Pacific Northwest. However, at this site the plant is larger than normal and growing faster than is typical of the native. Floating marsh pennywort does have a tendency to be 'weedy' occasionally here in Oregon and is a well-known invasive in Europe. We suspect this may be an ornamental cultivar of the native that may have escaped someone’s backyard pond, but don’t have any confirmation of that at this point.
Portland BES will be working with the appropriate agencies and land/dock owners to get some control work done in the next few weeks. Because the plants strong rhizomes are quite good at resprouting, I’d advise against pulling the plants out or disturbing these patches – doing so will risk spreading it to other areas of the docks or further downstream.
And please do upload a close-up if you have been able to take one. Thank you for taking the time to report this,
Vanessa Morgan
Portland State University-Center for Lakes and Reservoirs

Vanessa Howard Morgan
Sept. 24, 2013, 7:08 a.m.

I added few photos showing close-up shots of the plants (5 total). Hope this helps. -Dorie

Reporter
Sept. 24, 2013, 8:35 a.m.

Remedy

This species is native to the Pacific Northwest, but some recently discovered populations have shown invasive characteristics. Research is ongoing, and locations from this site will be useful in determining the status of these populations.

Location

The Portland Rowing Club is located at 100 SE Harney St in Portland, OR. just south of the Sellwood Bridge. The zip code is 97202. There is a large patch of an unknown invasive aquatic plant that is growing extremely fast in the water way between our North East Boat Slips and the river bank. It is growing several feet a day and has now completely blocked the water channel and is growing up the river bank. It is blocking the flow of debris through the channel as well. Floating home residents say that in the forty years that they have lived in this Portland Rowing Club houseboat community, they have never seen an aquatic plant like this. We need help identifying this plant and getting rid of it ASAP.

Expert Reviewer

Vanessa Howard Morgan

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