Canada waterweed is an underwater perennial. It grows in dense mats in clear waters. Most people know it as an aquarium plant. It is considered native to Nova Scotia and New Brunswick, but outcompetes native pond weeds in Island waterbodies. Canada waterweed was first detected in PEI at Knox’s Damn, Head of Montague, in 2005, and since then in Pondside Park, Stratford.
Here are some key features that may help to positively identify Canada waterweed:
- Leaves are oblong, green, translucent, and in whorls of 3 (occasionally 4) around the stem
- Leaves are 6-15mm long, 1-5mm wide and the leaf tips taper to a blunt point
- Canada waterweed is dioecious – male and female flowers occur on separate plants.
- Flowers are often not produced.
- From June to August, small white flowers occur on the ends of thread-like stalks, floating at the water surface.
- Fruit capsules, if produced, are 6mm long and ripen underwater.
- Reproduces mainly by stem fragments (stolons) and overwintering buds (short compact branches that appear in late summer)
- Stems are branched, round and slender, and can be 1 to several metres in length
- Flowers are white-pale purple and occur at the end of the stem, usually at or just below the water surface from June- August
- Depending on growing conditions, it can vary in appearance from being robust, bushy plants to spindly plants with very few leaves
- They produce adventitious roots which can hang free in the water or root at the water bottom.
Canada waterweed is considered a priority species for the PEI Invasive Species Spotters Network. If you see this plant, please report your sighting.
PEIISC factsheet on Canada waterweed