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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: dotted duckweed

Synonyms and Other Names: Lemna punctata, Spirodela punctata, Spirodela oligorrhiza

Taxonomy: available through www.itis.gov

Identification: Recent comprehensive review of morphological, biochemical and molecular data finds Spirodela punctata taxonomically distinct from other duckweeds (see Les and Crawford 1999). Although more closely related to Lemna than to Spirodela, this species has been reclassified under a new genus, Landoltia, in honor of Dr. Elias Landolt, world scholar on the Lemnaceae. It has also been referred to as Spirodela oligorrhiza.

Tiny free-floating aquatic plants comprised of individual fronds that produce fine roots. Mature fronds appear 1.5 to 2 times longer than wide, with widths measuring from 1-3 (or 5) mm. Fronds are narrowly egg-shaped to slightly kidney-shaped and intensely green in color. A waxy layer of cuticle makes plants sparkle in the sunlight. Fronds are not leaves; they may be a reduced form of stem and shoot. The roots number from 2-4 and can range up to 7. All of the roots penetrate the prophyllum (a scale surrounding the base of the frond that covers the point of attachment of the roots).

Propagation is mainly through vegetative budding of daughter fronds from two pouches at base of the frond. Daughter fronds often remain attached to mother frond by a short stipe so that plants often appear as a cluster of several fronds. This species occasionally reproduces sexually, by seed.

In the field, Landoltia punctata can readily be distinguished from native look-alike duckweed species, especially with the aid of a 10X hand lens. Lemna species will always have only 1 root per frond and are light green in color. Spirodela polyrrhiza has many roots (5-21); the frond is broad with nerves that are easily noticed and usually a red dot at the base of the nerves. Landoltia punctata is more elliptical and has several roots (2-4) per frond.

Comparison for distinguishing the non-native Landoltia punctata from the native Spirodela polyrrhiza

	Spirodela polyrrhiza	Landoltia punctata
Fronds	broadly ovate, almost as wide as long, mature fronds ~ 3-6 mm wide	narrowly egg-shaped, longer than wide, mature  fronds ~1-3 mm wide
Roots	numbering from 5-21 (commonly seen as 8-12), only 1 protrudes through the prophyllum	numbering from 2-5 (commonly seen as 3-4), all protrude through the prophyllum
Nerves	clearly visible, numbering 7-15 (commonly seen as 7-9 )	barely visible, numbering 3-7 (commonly seen as 3-5)
Color	usually with a red dot on upper frond	without a red dot on the upper frond

Side by side, these two species are easier to distinguish than when apart. Spirodela polyrrhiza is the largest duckweed and has more roots than others in North America. Landoltia punctata usually has several roots, generally fewer than S. polyrrhiza, but, always more than Lemna species, which only have one. Both Spirodela and Landoltia have reddish purple coloration on the undersurface of the fronds, a result of anthocyanin production, which varies with environmental conditions. The undersurface of Landoltia punctata is covered with many sunken glands (the reason for the epithet "punctata") that are seen as a heavier texture overall.

Size: 1-3 (5) mm wide

Native Range: Australia and Southeast Asia. Crawford and Landolt (1993) used enzyme electrophoresis to measure genetic diversity among Spirodela species. In Spirodela (Landoltia) punctata the highest diversity was found in biotypes from Australia and southeastern Asia. This supports the presumption of origin and species development in those regions, where early collection records also were made (Landolt 1986).

 Landoltia (Spirodela) punctata is sometimes reported as native to North America (BONAP 1999; USDA,NRCS 1999). However no evidence has been presented that refutes the extensive taxonomic and distribution studies conducted on this species (Landolt 1986). In reviewing more than 10,000 Lemnaceae specimens from North America, none of Landoltia punctata were found to predate the 1930 collection from Kansas City, Missouri (Saeger 1934), indicating the species as introduced to North America (Landolt 1986; E. Landolt, pers. comm. 1999).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Small, quiet, nutrient rich waters such as ponds, ditches, swamps and backwaters; also seasonally intermittent waters.

Climatic Limitations and Overwintering Potential: 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) (Landolt 1981). This concurs with the distribution mapped above, where Landoltia punctata ranges easily through the USDA cold hardiness Zone 7 ( USDA zone map east US;  west US;  AK, HI  ). Outlying occurrences in Pennsylvania, Illinois, Kentucky, Missouri and Oklahoma extend into Zone 6 and 5. Indeed, the species should be looked for in the Northeast (Crow and Hellquist 2000).

Under long-day photoperiods Landoltia punctata may sometimes form resting fronds. These are small, delicate single fronds with only one framentary root. High in starch, they function comparably to turions in that they are more capable than normal fronds in surviving unfavorable 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 (Landolt 1986).

Spirodela polyrrhiza, ranges widely in its native North America, extending to all U.S. states and far north of the Canadian border (Landolt 1981). While Landoltia punctata has a greater ability to set seed than does Spirodela polyrrhiza (0.1 percent of S. polyrrhiza found in fruit compared to 3 percent of L. punctata), the seeds of L. punctata are not known to tolerate cold temperatures (~ 0 degrees C for several weeks) (Landolt 1986). Therefore L. punctata cannot be expected to overwinter by seed in regions of the United States that are too cold for vegetative survival. However, the seeds tolerate drought. In Australia, L. punctata survives by seed in ponds that seasonally dry out (Landolt 1986). This mechanism could contribute to establishment in the arid southwestern United States.

Means of Introduction: In the 1800's, many of the known localities of Landoltia punctata outside of Australia and southeastern Asia were localized near harbors, suggesting very early dispersal among continents by humans (Landolt 1986).

Landoltia punctata is commonly used in aquaria and may be distributed when transporting fish or plants (Landolt 1986) so that even in the aquarium, the introduction one of the world's smallest flowering plants is often by accident (Stodola 1967). The Missouri pond first found with L. punctata also contained goldfish, suggesting the the plant might have been introduced from commercial supply sources for domestic aquaria (Daubs 1962). Its irregularity in distribution in the United States suggests multiple introduction sites. Water garden suppliers are an additional likely source.

Once escaped in a new region, Landoltia punctata can be transported short distances (several kilometers) by water birds, and less importantly by mammals like beavers, raccoons and wild hogs (Landolt 1986). However, duckweed fronds quickly desiccate once removed from the water, much more so than other small, floating plants, such as Salvinia. Wet feathers or rain may extend the distance of dispersal by birds, but generally fronds will dry out within 0.5 to 2.5 hr (Landolt 1986).

Status: Noted by many as expanding in range in North America; populations are overlooked because of its superficial resemblance to native duckweeds.

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic

Not known, although regarded as a pioneer species in that it is distributed easily, colonizes quickly and has a high rate of vegetative propagation (Landolt 1986).

Landoltia punctata, often occurs in extensive, almost pure stands while Spirodela polyrrhiza usually occurs in mixed populations, with other duckweed species (Godfrey and Wooten 1979; Davenport and Haynes 1981; Wohler et al 1965).

 In pure laboratory culture, Landoltia punctata grew at approximately twice the rate of Lemna minor (expressed as mg of dry weight per day in a 12 cm square area). Yet, in mixed cultures, no distinct competition effect was detected between the two (Ikusima 1955). In a competition study conducted in a north Florida swamp among the small floating plants, Salvinia minima (Baker), Landoltia punctata and Azolla caroliniana Willdenow, Landoltia punctata was found to be the most abundant species through the one-year study. Landoltia punctata was less affected than the other species by low winter temperatures and flooding while Salvinia minima dominated during the warm summer months (Dickinson and Miller 1998).

Remarks: Debate as to the correct nomenclature shifted from use of Lemna punctata G. Meyer, to Spirodela punctata (G. Meyer) C. H. Thompson, to Landoltia punctata (G. Meyer) Les & D. J. Crawford, to Spirodela oligorrhiza (Kurz) Hegelmaier, and back to Landoltia puncata (G. Meyer) Les & D. J. Crawford (Ward 2011; Wiersema 2014).

References: (click for full references)

Bishop Museum 1999. The Hawaiian Flowering Plants Checklist (http://www.bishop.hawaii.org/bishop). Hawaii Biological Survey, Bishop Museum, Honolulu, Hawaii.

BONAP 1999. Invasive Species Database Search (http://www.bonap.org). The Biota of North America Program, Universiy of North Carolina, Chapel Hill, North Carolina. 

Crawford, D.J. and E. Landolt. 1993. Allozyme studies in Spirodela (Lemnaceae): variation among conspecific clones and divergence among the species. Systematic Botany 18(3):389-394

Crow, G.E. and C.B. Hellquist. 2000. Aquatic and Wetland Plants of Northeastern North America. Vol. II. Monocotyledons. The University of Wisconsin Press, Madison, Wisconsin. Pp. 82-83.

Daubs, E.H. 1962. The occurrence of Spirodela oligorrhiza (Kurz) Hegelm in the United States. Rhodora 64: 83-85.

Davenport, L.J. and R.R. Haynes. 1981. Aquatic and marsh plants of Alabama II. Arecidae. Castanea 46:291-299. 

Dickinson, M.B., and T.E. Miller. 1998. Competition among small, free-floating, aquatic plants. American Midland Naturalist 140(1):55-67. http://links.jstor.org/sici?sici=0003-0031%28199807%29140%3A1%3C55%3ACASFAP%3E2.0.CO%3B2-R.

Ikusima, I. 1955. Growth of duckweed populations as related to frond density. Physiol. Ecol. Jap. 6:69-81. 

Jones, S.B. Jr. 1974. Mississippi Flora. I. Monocotyledon Families with Aquatic or Wetland Species. Gulf Research Reports 4(3)357-379.

Harrison, D.E. and E.O. Beal. 1964. The Lemnaceae (duckweeds) of North Carolina. Journal of the Elisha Mitchell Science Society. 80:12-18.

Landolt, E. 1981. Distribution pattern of the family Lemnaceae in North Carolina. Veroff. Geobot. Inst. ETH, Stiftung Rubel. No. 77, pp. 112-148.

Landolt, E. 1986. The family of Lemnaceae - a monographic study. Vol 1. In: Biosystematic Investigations in the Family of Duckweeds (Lemnaceae). Veroff. Geobot. Inst. ETH, Stiftung Rubel. No. 71.

Landolt, E. 1997. How do Lemnaceae (duckweed family) survive dry conditions? Bulletin of the Geobotanical Institute ETH. 63: 25-31.

Les, D.H. and D.J. Crawford. 1999. Landoltia (Lemnaceae), a new genus of duckweeds. Novon 9: 530-533.

Montz, G.N. 1979. Distribution of selected aquatic species in Louisiana (a report dated Sept. 1979). US Army Corps of Engineers, New Orleans, Louisiana.

Nelson, E.N. and R. W. Couch. 1985. Aquatic Plants of Oklahoma I: submersed, floating-leaved, and selected emergent macrophytes. Oral Roberts University. Pp. 91.

Saeger, A. 1934. Spirodela oligorrhiza collected in Missouri. Bull. Torr. Bot. Club 61: 233-236.

Steury, B. 2000. Noteworthy Collections: Maryland. Castanea 65(3)228-229.

USDA, NRCS 1999. The PLANTS database (http://plants.usda.gov/plants). National Plant Data Center, Baton Rouge, Louisiana.

Ward, D.B. 2011. Spirodela oligorrhiza (Lemnaceae) is the correct name for the lesser greater duckweed. Journal of Biogeography 5(1):197-201. https://www.jstor.org/stable/41972506.

Wiersema, J.H. 2014. Application of the name Lemna punctata G. Mey., the type of Landoltia Les & D. J. Crawford. Plant Biology 17(s1):5-9. https://doi.org/10.1111/plb.12209.

Wohler, J.R., I.M. Wohler and R.T. Hartman. 1965. The occurrence of Spirodela oligorrhiza in Western Pennsylvania. Castanea 30: 230-231.

Yatskievych, G. 1999. Steyermark's Flora of Missouri. Vol. 1. The Missouri Department of Conservation, Jefferson City, Missouri, in cooperation with the Missouri Botanical Garden press, St. Louis, Missouri. Pp. 487-488.

Additional Data Sources:

Beal, E.O. and J. W. Thieret. 1,986 Aquatic and Wetland Plants of Kentucky Kentucky Nature Preserves Commission, Scientific and Technical Series 5

Bioinformatics Working Group 1999. Texas A&M University Bioinformatics Working Group, The Texas Flora, Herbarium Specimen Browser (http://www.csdl.tamu.edu/FLORA).

Brown, E.T. and R. Athey. 1992. Vascular Plants of Kentucky an Annotated Checklist. University Press of Kentucky.

Gabrielson, F.C., Jr., A.M. Malatino and G.J. Santa Cruz. 1980. Correlation of seasonal variations in phosphorous and nitrogen species in Upper Black Warrior River with duckweed. National Technical Information Service, Springfield, VA. 6-77-01

Hill, S.R. and C.N. Horn. 1997. Additions to the Flora of South Carolina Castanea 62(3):194-198.

Mohlenbrook, R.H. 1986. Guide to the Vascular Flora of Illinois. Southern Illinois University Press.

Simmons, M.P., D.M.E. Ware, and W.J. Hayden. 1995. The vascular flora of the Potomac River watershed of King George County, Virginia. Castanea 60(3):179-209.

Smith, E. 1988. An Atlas and Anotated List of the Vascular Plants of Arkansas (www.csdl.tamu.edu/FLORA/arkansas) University of Arkansas.

Smith, L. 1978. Development of the emergent vegetation in a tropical marsh (Kawainui, I'ohu). Newsletter of the Hawaiian Botanical Society. 17.

Specimen Management System for California Herbaria - SMASCH (htttp://www.mip.berkeley.edu/www_apps/smasch/)

Thomas, R.D. and C.M. Allen. 1,993 Atlas of the Vascular Flora of Louisiana. Vol I: Ferns and Fern Allies, Conifers, and Monocotyledons. Moran Colorgraphic Printing, Baton Rouge, LA.

USDA, NRCS. 1997. The PLANTS database (http://plants.usda.gov), National Plant Data Center, Baton Rouge, Louisiana 70874-4490.

Wunderlin, R.P., B.F. Hansen, and E.L. Bridges. 1995. Atlas of Florida Vascular Plants (http://www.usf.edu) Institute for Systematic Botany, University of South Florida.

The curators of the following herbaria are acknowledged for providing specimen voucher data: Delaware State University Herbarium (DOV); Deaver Herbarium (NAU) of Northern Arizona University; Northeast Louisiana University Herbarium (NLU), University of Georgia (GA), Morris Arboretum (MOAR) Pennsylvania Flora Project Database.

Author: Jacono, C.C., and I.A. Pfingsten

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.