Invasive Plant Guide

Congratulations to Virginia on its new laws regulating invasive ornamental plants!   A list of 39 species, if sold at a retail nursery, will have to be labeled to inform consumers that they are potentially invasive.  Some provisions of the law do not take effect until January, 2027. https://lis.virginia.gov/bill-details/20251/HB1941

Maryland updated its law listing ornamental invasive plants in June 2024 making it easier to add new species to the list, although as of April, 2025, there don’t appear to have been any new additions. Maryland has a two-tiered list with some plants banned from sale, and some requiring labeling at retail nurseries. https://extension.umd.edu/resource/invasive-plants-avoid-buying-your-yard-and-garden-maryland/

My dad was out kayaking on a slough near Newport, OR with some botanists and learned

Japanese eelgrass rests on the muddy edge of a slough near Newport, OR.

about Japanese (or dwarf) eelgrass, Zostera japonica.  It often occurs in the same locations as the native common eelgrass, Z. maritima, but higher in the intertidal if both species are present.  It has narrower and shorter leaf blades than common eelgrass.

Japanese eelgrass probably arrived in the 1930s in shipments of Pacific oysters.  It reproduces prolifically by seed and spreads by rhizomes.  It has established from Humboldt Bay in CA north to the Strait of Georgia in Canada.

You can read an excellent summary about this eelgrass written by Levy Hay at University of Washington in 2011.

In another couple months the tumbleweeds will be rolling along in the western United States.  Wells and Ellstrand (2016) at the University of California – Riverside documented a new hybrid species of tumbleweed, Salsola ryanii, rapidly expanding its range.  Salsola ryanii is an allopolyploid species with 2 complete sets of genes from its parent species, S. tragus and S. australis.

Spring is here and along with it some of the more edible invasive plants.  Anyone for a dish of knotweed kimchi or garlic mustard pesto pasta?  Pittsburgh has gone to great lengths developing edible uses for Japanese knotweed, Fallopia japonica.   One business sells it by the pound to enterprising brewers and bakers.  Watch a video from the Wall Street Journal on Pittsburgh’s knotweed gourmets here, http://on.wsj.com/1YRN9g2.

The ultimate online resource for eating invasive plants (and animals) is probably Eat the Invaders.  Here you can find all sorts of information and recipes on edible invaders.  Bon appetit!

According to the Virginia Department of Conservation and Recreation Murdannia has no known common name and generally goes by Anielema, its former Latin name.  The USDA PLANTS website calls it wartremoving herb and Invasive.org calls it marsh dayflower.  Maryland Extension calls it marsh dewflower or Asiatic dayflower.  The leaves and stems do resemble Asiatic dayflower (Commelina communis).  I don’t know about it’s wart-removing powers.

Murdannia keisak in a marsh on the Maryland Coastal Plain.

Look for mats of Murdannia keisak in freshwater ponds and marshes and along the edges of streams and canals.   It probably arrived in the US from eatern Asia in the 1920s or 30s as a weed of rice cultivation but it has unfortunately spread to natural areas.  It forms dense mats blocking light to plants below. Plants produce thousands of small seeds eaten by ducks and other waterfowl, and the plants spread vegetatively.

Small stands could be hand-pulled before flowering taking care to remove all fragments of the plant.  Larger stands are usually treated using biodegradable herbicides.

Wallace Kaufman pauses on the battlefield

Wallace Kaufman and Knot-weed stalks

April 24, 2015. Along the west bank of Poole Slough, 4 miles east of the Pacific Ocean and Newport, OR.  Here begins the first battle of the third year against the dense stand of giant knotweed that took over about an acre of land where an old barn and a few apple trees stood 60 years ago. When the first battle began in late summer 2012 the knotweed stood in an almost pure stand, stalks up to 10 feet high and two inches thick, two or three stalks from one root, plants 6 to 12 inches apart. Although I cut before they flower, the roots send out new stalks all summer and again in the spring. The stalks are hollow cylinders closed off at knots every 6 to 12 inches. Dried stalks make good pan pipes and flutes. Fresh young stalks can be peeled and cooked as vegetables.

Since the plants begin storing carbohydrates in the roots in early summer, I’ll cut again then and again in the fall. As the lower growing natives begin to compete, the prospects are that I can begin regular mowing with a blade set high to allow low natives to grow while preventing the knotweeds from replenishing their roots.

Each year the stand has been slower growing, stalks slimmer, and height diminished. Here is a scene from the very first attack 3 years ago.