Ducklettuce (Ottelia alismoides)

Synonyms: Stratiotes alismoides, Damasonium alismoides, Ottelia indica

Description:

Ducklettuce (Ottelia alismoides) is a submersed aquatic plant from the fresh waters of Asia and northern Australia [1][3]. It has turned up in a few southern U.S. states, probably arriving as seeds mixed in rice shipments and carried by waterfowl [1][2]. It is on the U.S. federal noxious weed list and is still uncommon here, so MISIN tracks it closely ? catching new populations early is the best chance to keep it from spreading [1].

Habit:

Ducklettuce is a submersed (underwater) plant that grows as a rosette of leaves rising from the bottom of still or slow fresh water [1][2]. Its leaves are thin and see-through, oval to heart-shaped, with a distinctive "quilted" look ? fine ribs run both lengthwise and crosswise across the blade [2]. In warm months it sends up single flowers on long stalks that reach the water surface; each flower has three petals, usually white with a yellow center, and opens from a ribbed green sheath [1][2]. It is easiest to spot when these flowers reach the surface; the rest of the year it is easy to miss among other underwater plants [2]. Ducklettuce is a federally regulated noxious weed and is uncommon in the United States, so any sighting is worth reporting [1].

At-a-glance cues:

1. Underwater rosette of thin, see-through leaves with a quilted look from lengthwise and crosswise ribs [2]
2. Oval to heart-shaped leaf blades on long stalks [2]
3. Single white (sometimes pink-purple) three-petaled flowers with a yellow center, rising to the surface on long stalks in warm months [1][2]
4. Grows in still or slow fresh water ? ponds, ditches, lake edges, and marshes [1]

Leaves:

1. Arrangement: in a basal rosette rising from the bottom; mostly submersed, sometimes reaching the surface in shallow water [1][2]
2. Shape: young leaves narrow; mature leaves oval to broadly heart-shaped, on long stalks [2]
3. Size: blades about 4 to 6 inches (11?16 cm) long, on stalks up to about 20 inches (50 cm) [2]
4. Surface: thin and translucent with a quilted look, from ribs running both lengthwise and crosswise [2]
5. Margin: smooth to finely toothed [2]

Stems:

1. Habit: a submersed aquatic plant with no upright leafy stem; leaves and flower stalks rise from a short base at the bottom [1][2]
2. Roots: anchored by fine roots in the mud; plants can break free and float [1]
3. Spread: no runners or other creeping parts ? it spreads only by seed [1]

Flowers:

1. Structure: a single flower rises to the surface inside a ribbed, cylindrical green sheath (spathe) about 1 inch (2?4 cm) long [2]
2. Color: 3 petals, usually white (sometimes pink, blue, or purple), with a yellow base [1][2]
3. Arrangement: borne one at a time on a long stalk reaching the water surface [2]
4. Bloom time: the warm months of the growing season [2]
5. Sex: flowers can pollinate themselves, setting seed even on a lone plant [1]

Fruit and seeds:

1. Fruit type: a fleshy, ribbed capsule formed inside the spathe [1][2]
2. Seed count: a single plant can make up to about 2,000 small seeds [1][2]
3. Seeds: tiny, oval, and ribbed [1]
4. Viability: seeds can stay alive in the sediment for up to about four years [1]
5. Dispersal: seeds spread in water and mud, on boats and gear, and in shipments of rice and other goods [1][2]

Habitat:

Ducklettuce grows in still or slow-moving fresh water ? ponds, marsh pools, lake edges, irrigation ditches, stream margins, and rice paddies ? usually in water from a couple of inches to about 3 feet deep [1][2]. It is native to Asia and northern Australia [1][3]. In North America it has been found in a handful of southern states, including Texas, Louisiana, Arkansas, Florida, and Missouri; an early California population was eradicated [1][4]. It can break free of the mud and float, which helps it move to new spots [1].

Reproduction:

Ducklettuce spreads only by seed ? it has no runners or other creeping parts [1]. A single plant can make up to about 2,000 tiny seeds, which can stay alive in the mud for up to four years before sprouting [1]. The seeds travel in water and mud, on boats, trailers, nets, and other wet gear, and they have been carried long distances in shipments of rice and other goods [1][2]. The flowers can even pollinate themselves, so a lone plant can set a full crop of seed [1]. Because it lives one season and relies entirely on seed, removing plants before the flowers set seed is the key to stopping it [2].

Impact and Damage:

Ducklettuce is not known to be toxic to people or pets [1]. Its main concern is as a water weed: dense underwater stands can crowd a pond, tangle boats and fishing lines, and make swimming and paddling difficult [2]. In Asia it is a weed of rice paddies, where it competes with the crop [2].

In North America its impacts have not yet been well studied, because it is still rare here [1]. The worry is what it could do if it spread: thick underwater growth could shade out and crowd native water plants, lower water quality, and reduce the variety of life in a pond or marsh [2]. That risk is why it was placed on the federal noxious weed list before it became widespread ? the goal is to stop it early [1].

Similar species:

Underwater, ducklettuce can be mistaken for other broad-leaved water plants; the quilted, see-through leaves and the surfacing white flowers help set it apart.

European frogbit (Hydrocharis morsus-ranae) is an invasive water plant with small white three-petaled flowers and a yellow center much like ducklettuce, but its kidney-shaped leaves float flat on the surface in rosettes rather than staying submerged [2].

Broad-leaved pondweeds (Potamogeton species) have similar thin, translucent underwater leaves, but their tiny flowers are packed into a small spike held just above the water rather than the showy white petals of ducklettuce [2].

Monitoring and rapid response:

Signs to watch for:

1. Underwater rosettes of thin, quilted, see-through leaves in still or slow fresh water [2]
2. Single white (sometimes pink-purple) three-petaled flowers with a yellow center floating at the surface on long stalks in warm months [1][2]
3. Plants in ponds, ditches, marshes, or rice fields, sometimes floating free after breaking loose [1]

What you can do:

1. For a few plants in a small pond, hand-pull them, gently lifting the whole plant and its roots out of the water before the flowers set seed [2].
2. Bag the pulled plants and dispose of them on dry land well away from any water so seeds cannot wash back in [2].
3. Clean, drain, and dry boats, trailers, nets, waders, and other gear before leaving the water so you do not carry seeds to a new place [2].
4. Because this is a federally regulated noxious weed that is still rare here, the most useful step is to report it right away (see below) so trained crews can respond while the population is small [1].
5. Natural-area and water managers handle larger or established sites ? mapping the population, removing plants before seed set, and monitoring for several years because the seeds last in the sediment [1][2].

When to call a professional:

1. Any suspected population beyond a few plants, or any infestation in a lake, river, or shared waterway, where federal and state agencies coordinate the response to this regulated weed [1].
2. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. U.S. Geological Survey, Nonindigenous Aquatic Species Database. Ottelia alismoides (duck-lettuce) species profile. nas.er.usgs.gov
2. University of Florida IFAS, Center for Aquatic and Invasive Plants. Ottelia alismoides (duck-lettuce). plant-directory.ifas.ufl.edu
3. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. Ottelia alismoides (L.) Pers. powo.science.kew.org
4. USDA NRCS Plants Database. Ottelia alismoides (L.) Pers. (duck-lettuce, symbol OTAL). plants.usda.gov

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