Photo credit: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Species at a Glance
Curly-leaf pondweed is an invasive aquatic perennial that can grow offshore in depths of up to 4.6 m (15 ft). It has a unique ability to form new plants under the ice in winter, making it one of the first nuisance plants to emerge in the spring.
Leaves: Submerged, oblong, slightly translucent, leaves are olive-green to reddish-brown and have rounded tips, narrowing towards the base. They are alternately arranged and directly attached to the stem. They are 4-10 cm (1.6-4 in) long and 5-10 mm (0.2-0.4 in) wide with distinct wavy and finely toothed edges that resemble lasagna noodles.
Flowers: Small and tightly arranged flowers are located at the end of a slender, sometimes curved, stalk and appear above the water’s surface from June through September.
Fruits/Seeds: Have a prominent cone-shaped beak and a bumpy crown-like ridge.
Stems/Roots: Slightly flat, reddish-brown stems grow from 0.3-0.9 m (1-3 ft) long and emerge from slender rhizomes, often branching as they grow giving it a bushy appearance.
This species may be confused with other pondweeds, many of which have both emergent and submerged leaves. Curly-leaf pondweed has only submerged leaves. Other pondweeds also lack the tiny but visible serrations and wavy edges of the leaves.
Curly-leaf pondweed prefers soft substrates in shallow, alkaline, and high nutrient waters. It tolerates still or flowing water and is able to survive in low light conditions and water temperatures. It can grow in shaded, polluted, disturbed, or turbid waters where many native plants cannot.
Burr-like winter buds called turions allow curly-leaf pondweed to regrow in new locations when they are moved around by natural water flow, recreational activities such as boating and fishing, and by intentional plantings for wildlife habitat. It can also reproduce and spread by seeds which are ingested by waterfowl and can pass through the digestive system unharmed.
Native to Eurasia, Africa, and Australia, curly-leaf pondweed was introduced into U.S. waters by hobbyists who used it as an aquarium plant. It has since spread to all states and is widespread throughout the Mid-Atlantic region.
Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.
Because of its tolerance for low light and temperature conditions, curly-leaf pondweed grows earlier than native plants in the spring. It forms dense surface mats that can impede recreational activities such as boating, swimming, and fishing. When it dies off in mid-summer, it may create anoxic conditions and increase nutrient content that can cause harmful algal blooms.
Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).