Taxonomic name: Landoltia punctata (G. Mey) Les & D.J. Crawford
Synonyms: Lemna melanorrhiza F. Muell. ex Kurz in J. Bot. 5 (1867), Lemna oligorhiza Kurz in J. Linn. Soc. London 9 (1866), Lemna pleiorrhiza F. Muell. ex Kurz in J. Bot. 5 (1867), Lemna punctata G. Mey., Prim. fl. Esseq. (1818), Spirodela javanica (Bauer) Hegelm. in Bot. Jahrb. Syst. 21 (1895), Spirodela melanorrhiza (Kurz) Hegelm. in Bot. Jahrb. Syst. 21 (1895), Spirodela oligorrhiza (Kurz) Hegelm., Lemnaceen (1868), Spirodela pleiorrhiza Hegelm. in Bot. Jahrb. Syst. 21 (1895), Spirodela punctata (G. Mey.) Thompson in Rep. Missouri Bot. Gard. 9 (1897), Spirodela pusilla Hegelm. in Bot. Jahrb. Syst. 21 (1895)
Common names: dotted duckmeat (English), dotted duckweed (English), giant duckweed (English)
Organism type: aquatic plant
Native to Southeastern Asia and Australia and arguably to the United States, Landoltia punctata (dotted duckweed) has been introduced to several states in the U.S.A. and many European and Asian countries. It thrives in nutrient rich waters and prefers slow moving or stagnant ponds to enhabitat. Consequences of its introduction are unknown, but its capability to reproduce quickly, disperse rapidly and grow in low oxygen areas make it a potential threat to freshwater systems.
Landoltia punctata is a small, free-floating plant that has fronds which produce thin roots. The plants can grow into dense mats in stagnant water. (CAIP, 2002). Mature fronds are 1.5 to 2 times longer than wide, with widths between 1-5mm. Fronds are narrowly egg-shaped to slightly kidney-shaped and intensely green in colour. The name punctata comes from the sunken glands on the undersurface of the fronds. Fronds are not leaves; they may be a reduced form of stem and root. A waxy cuticle covers the fronds causing a sparkle when sunlight hits them; they also have a reddish-purple tint on the underside of the fronds due to anthocyanin production. L. punctata normally has between 2-4 roots but can have as many as 7.
L. punctata is distinguished by its reduced frond prophyllum, root tracheids, external anther locules, and also by well-supported molecular evidence provided by allozymes and cpDNA sequences. (Les & Crawford, 1999). "All of the roots penetrate the prophyllum (a scale surrounding the base of the frond that covers the point of attachment of the roots)." (Jacono, 2002). “Many duckweeds, including our native Spirodela polyrrhiza, survive climate in cold regions by forming an abundant supply of turions (rootless fronds rich in starch) that sink to the warm bottom to overwinter. The inability of Landoltia punctata to form turions accounts for its absence in the northern and Midwestern United States. Its fronds are sensitive to severe frosts and plants are reportedly limited by absolute minimum temperatures <- 20 C (- 4 F). Under long-day photoperiods Landoltia punctata may sometimes form resting fronds. These are small, delicate single fronds with only one fragmentary root. High in starch, they function comparably to turions in that they are more capable than normal fronds in surviving unfavourable conditions such as storms and light frost. However, they do not sink to the bottom and thereby do not provide overwintering protection in zones with severe winters.” (Jacono, 2002). L. punctata can survive drought by seed in arid regions such as Australia, which has led experts to believe that it has the potential to become established in arid southwestern US states. (Jacono, 2002).
lakes, water courses, wetlands
L. punctata prefers "small, quiet, nutrient rich waters such as ponds, ditches, swamps and backwaters; also seasonally intermittent waters." (Jacono, 2002).
Jacono (2002) states thatL. punctata's impacts are generally unknown, but that it has the potential to become a serious nuisance due to its rapid colonization, easy distribution, and quick dispersal rate.
Valued as a waste water cleanup mechanism, L. punctata is grown on farms and in aquatic systems to clean/purify high nutient bodies of water." (Hanelt, 2001). Chaiprapat et al (2005) state that "Spirodela punctata 7776 can remove N (mainly ammonium and P from anaerobically pretreated swine wastewater at rates as high as 2.32 and .51 g/m²/day (23.2 and 5.1kg/ha/day), respectively, under the climatic conditions of Raleigh, NC." It is also harvested as a substitute for alfalfa in cow and pig diets. (Hanelt, 2001). Because of its high Nitrogen content, it could also be used as a fertilizer. (Chaiprapat et al, 2005).
After escape, L. punctata can be vectored by waterfowl, but less likely by raccoons, beavers and wild hogs. However, they die rapidly once removed from the water, drying out with 1/2 to 21/2 hours. (Jacono, 2002).
Native range: Africa; Macaronesia: Spain - Canary Islands (Tenerife); Northern Africa: Egypt; South Tropical Africa: Zimbabwe; Southern Africa: South Africa - Cape Province, Natal, Transvaal; Western Indian Ocean: Madagascar; Mauritius; Asia-Temperate: Western Asia: Israel; China: China - Fujian, Henan, Hubei, Jiangsu, Sichuan, Yunnan, Zhejiang; Eastern Asia: Japan - Honshu, Kyushu, Shikoku; Taiwan; Asia-Tropical: Indian Subcontinent: India; North Indian Ocean: Maldives; Indo-China: Thailand, Malaysia: Indonesia; Malaysia; Philippines; Australasia: Australia: Australia - New South Wales, Queensland, South Australia, Tasmania, Victoria, Western Australia, New Zealand: New Zealand; Pacific: Southwestern Pacific: Fiji; New Caledonia; Vanuatu; Southern America: Northern South America: Guyana; Venezuela, Brazil: Brazil - Rio de Janeiro, Sao Paulo, Western South America: Colombia, Southern South America: Argentina - Tierra del Fuego; Chile. (USDA-ARS, 2006).
Known introduced range: United States (Jacono, 2002)
Introduction pathways to new locations
Agriculture: Landoltia punctata is introducted to nutrient filled waste water ponds as a means to absorb excess nutrients. Also, L. punctata could potentially be utilized as a fertilizer. (Chaiprapat et al, 2005)
Pet/aquarium trade: L. punctata was introducted via the aquarium trade to the USA. (CAIP, 2002).
Chemical: Diquat is a widely used and effective herbicide because it causes ion leakage in duckweed and other aquatic plants. A Florida study showed that after 20-30 years, Landoltia punctata developed resistance to Diquat and Paraquat herbicides. The mechanism of resistance to Diquat is independent of electron transport in photosynthesis, and therefore is not exclusive to photosynthesis. (Koschnick et al, 2006). A separate study by Koshnick et al (2004) indicated that Landoltia punctata was not adequately controlled by Carfentrazone-ethyl at the maximum proposed rate of 224g/ha Super(-1).
Landoltia punctata reproduces via vegetative budding of the daughter fronds from the two pouches at the base of the frond. Daughter fronds stay attached to mother fronds by a short stipe, which gives a cluster-like appearance to the plant. L. punctata can also reproduce sexually, by seed, but this occurs seldomly. (Jacono, 2002).
Reviewed by: Expert review underway: Tyler J. Koschnick, PhD
Aquatics Research Manager
SePRO Corporation USA
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Wednesday, 8 November 2006