Taxonomy: Family-Lemnaceae (Duckweed Family); Order-Arales;
Subclass-Arecidae; Class-Liliopsida (Monocotyledons); Division-Magnoliophyta.
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.
Identification: 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. Take
this link to a comparison page for distinguishing the nonnative Landoltia
punctata from the native Spirodela polyrrhiza.
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).
Habitat: Small, quiet, nutrient rich waters such as ponds,
ditches, swamps and backwaters; also seasonally intermittent waters.
Nonindigenous Occurrences: First documented in North America
at two locations in Missouri (Saeger 1934); presently known from a limited
distribution in that state (Yatskievych 1999). Well naturalized in the southeastern
United States, notably in Florida and Georgia. Common in ponds
and still waters throughout Alabama (Davenport and Haynes 1981). Abundant
in late summer and autumn at scattered locals in southwest Mississippi (Jones
1974). Abundant throughout Louisiana, at lakes, bayous and fresh
marshes (Montz 1979). Extending northward, especially through drainages of the
Lower Mississippi River in Arkansas, Tennessee, and Kentucky.
Widely scattered in east Texas and into Oklahoma (Nelson and
Couch 1985). Eliminated at one of two known locals in Arizona - Lindberg
Springs, just south of Flagstaff, was the only known locality for wild rice
(Zizania) in the state of Arizona, but weeds and all perished when
it was siphoned dry to irrigate a golf course (T. Ayers, Deaver Herbarium pers.
comm. 2000). First discovered on the west coast in California during
the 1950s near Berkeley (Mason 1957), but not collected in southern California
until 30 years later (Armstrong 1984). Northern occurrences include Clatsop
County, Oregon (Landolt 1986), Illinois (Daubs 1962), western
Pennsylvania (Wohler et al. 1965) and eastern Massachusetts (Landolt
1986). First reported for North Carolina in 1964 where it has spread
rapidly to become locally abundant in widely scattered locations of the Coastal
Plain and Piedmont (Harrison and Beal 1964; Harrison 1977). Collected in south
eastern North Carolina, June 2002, associated and entangled with Salvinia
molesta [Kay s.n. (NCSU)]. Rather frequent around the District of Columbia
(Landolt 1986), yet reported in 2000 as new
to Maryland, along a creek head in Aberdeen Proving Grounds (Steury 2000).
Documented for Delaware in 1991 at Lums Pond State Park, in the Brandywine-Christina
drainage (DOV 19761). Naturalized on the islands of Oahu and Hawaii, Hawaii
(Bishop Museum 1999).
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: 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).
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).
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.
References:
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.
Bishop Museum 1999. The Hawaiian Flowering Plants Checklist (http://www.bishop.hawaii.org/bishop).
Hawaii Biological Survey, Bishop Museum, Honolulu, Hawaii.
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.
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: C.C. Jacono
Revision Date: 13 June 2002
