Duckweed Lemna Species: The Full List, and Why It Moves
The duckweed genus Lemna holds 13 to 15 species, depending on who counts. The full list by section, the two hybrids, and why the number keeps changing.
Ask how many duckweed Lemna species exist and you get a different number from every reference you open. The US Department of Agriculture lists 9. The Integrated Taxonomic Information System lists 8. World Flora Online says about 15. The specialists who maintain the duckweed community roster list 14 names, two of which are hybrids.
None of these sources is careless. They disagree because the genus Lemna is still being worked out, and the parts that are moving are precisely the species people grow, test and cite most often. This page gives the full roster organised the way the molecular evidence supports, then explains why the number moves and what that means if you are about to pick a Lemna species for a system or reuse a figure someone else published.
How many Lemna species are there?
The working answer from the duckweed specialists is 13. A 2016 taxonomy review counted 37 duckweed species in five genera, 13 of them in Lemna, alongside Spirodela, Landoltia, Wolffiella and Wolffia. The same review gives the rule that defines the genus: Lemna fronds carry one root. SERAPH works with that same family scope of about 37 species across five genera.
The other counts come from different decisions about the same plants:
| Source | Lemna count | What drives the difference |
|---|---|---|
| USDA PLANTS | 9 | Only species recorded in the United States |
| ITIS | 8 | US scope, record last reviewed in 2010 |
| Sree, Bog and Appenroth 2016 | 13 | Global, counts L. japonica as a species |
| Charm of Duckweed roster | 12 plus 2 hybrids | Lists L. x japonica and L. x mediterranea as hybrids |
| World Flora Online | about 15 | Includes names the specialists do not list |
That last row is worth a second look. The World Flora Online list includes L. landoltii and L. bistrosa, neither of which appears on the specialist roster, and it leaves out L. yungensis, which does. Even the family total has drifted: the updated 2020 determination key works with 36 accepted duckweed species, one fewer than the 2016 review.
The Lemna species list, section by section
Lemna is split into sections, and the sections are more stable than the species inside them. A combined molecular and morphological phylogeny found four of them, Lemna, Uninerves, Alatae and Biformes, to be well-defined clades, each with 100 percent bootstrap support. Section membership below follows the Wayne’s Word species list; common names are the USDA ones where the species occurs in the US.
| Species | Section | Common name |
|---|---|---|
| Lemna minor | Lemna | common duckweed |
| Lemna gibba | Lemna | swollen duckweed |
| Lemna turionifera | Lemna | turion duckweed |
| Lemna obscura | Lemna | little duckweed |
| Lemna disperma | Lemna | none in USDA |
| Lemna trisulca | Lemna | star duckweed |
| Lemna x japonica | Lemna (hybrid) | none in USDA |
| Lemna x mediterranea | Lemna (hybrid) | none in USDA |
| Lemna minuta | Uninerves | least duckweed |
| Lemna valdiviana | Uninerves | valdivia duckweed |
| Lemna yungensis | Uninerves | none in USDA |
| Lemna aequinoctialis | Alatae | lesser duckweed |
| Lemna perpusilla | Alatae | minute duckweed |
| Lemna tenera | Biformes | none in USDA |
Section Lemna
The big one, and the one that matters most in practice. It holds Lemna minor, the default organism of the duckweed literature, together with L. gibba, L. turionifera and both known hybrids. Star duckweed, L. trisulca, used to sit in a section of its own called Hydrophylla. The 2002 phylogeny found that section had no phylogenetic integrity and recommended moving L. trisulca into section Lemna, where it is distinctive in form but nests firmly inside the clade.
Section Uninerves
Small, one-veined species: L. minuta, L. valdiviana and L. yungensis. The single nerve is the diagnostic character, against 3 to 7 nerves elsewhere in the genus. Genetically this section stands well apart. Its defining branch was longer than that of every duckweed genus except Spirodela, and the authors wrote that raising sections like this one to genus rank “merits serious consideration”.
Section Alatae
L. aequinoctialis and L. perpusilla, recognised by root sheaths that are winged at the base. This is also the least settled corner of the genus, covered below.
Section Biformes
A single species, L. tenera. It rarely features outside taxonomic work, but it is one of the four clades the phylogeny supports.
Why the count keeps moving
Three separate things push the number around. None of them is a mistake in any one database.
Old names that refuse to die
Several Lemna names were retired decades ago and are still in active use. The 2016 review documents the main ones: L. paucicostata and L. aoukikusa are synonyms of L. aequinoctialis, L. minuscula is now L. minuta, and L. ecuadoriensis was merged into L. obscura in 2000. That last merger was missed by a major 2002 paper and the error propagated, which is why the family is still sometimes quoted at 38 species instead of 37. Names like “Lemna polyrhiza” and “Lemna arrhiza” are not valid Lemna at all, because those plants have more than one root or none, and they belong to Spirodela and Wolffia.
Common names are worse. ITIS gives “least duckweed” to both L. minor and L. minuta, and “lesser duckweed” to both L. minor and L. aequinoctialis. A common name tells you what a plant looks like, not what it is.
Hybrids hiding inside section Lemna
This is the real driver. In 2025, chromosome-level genomes showed that L. japonica is a set of L. minor by L. turionifera hybrids, occurring as both diploids and triploids. It was described as a species, it is still counted as one in some lists, and it is a hybrid.
L. x mediterranea is the second. It is a cross between L. minor and L. gibba, described in 2024 with two cytotypes, diploid and triploid, arising from at least two independent hybridisation events. The authors concluded that no single morphological character is enough to identify it. It was first found in old culture collections, and only in 2025 was it recorded growing wild, at five sites across roughly 4,200 square kilometres in Campania, the same area where an Italian botanist had described a “Lemna symmeter” about fifty years earlier. The two turned out to be the same plant.
Hybrids explain why reference collections have been so often wrong. A genotyping survey of section Lemna in the Landolt collection found an overall morphological misidentification rate of 28.6 percent, and 36 percent of clones labelled L. minor were in fact L. x japonica. Regional floras show the same pattern from the field side: the Washington State checklist notes that many specimens filed as L. minor are actually L. turionifera, which appears to be far more common there.
Section Alatae is still being sorted out
The tropical L. aequinoctialis group is the open frontier. A 2025 study of 52 Alatae accessions found ploidy variation, recurrent hybridisation and backcrosses between species and their hybrids, with the hybrids spread over three continents. Unusually for duckweed, some of these accessions flower and set viable seed readily, which gives the group a route to new combinations that the mostly clonal rest of the genus rarely uses. Expect the names in this section to change again.
The Lemna species you are most likely to meet
In Europe and North America, most Lemna on a pond surface is one of five: L. minor, L. gibba, L. turionifera, L. minuta or L. trisulca. The British botanical society’s crib gives the practical separations. L. gibba is usually larger and rounder with a swollen underside, but in cold, stagnant or nutrient-poor water the swelling may not develop, and the fronds then pass for L. minor. L. minuta has 0 to 1 vein against 3 in L. minor. L. turionifera shows a row of small bumps along the upper midline, is often red underneath, and forms rootless resting buds. The same source records L. minuta spreading through southern Britain and L. turionifera spreading in central Europe.
That last trait is the one to remember. In the 2025 genome study, L. turionifera readily formed duckweed turions while none of the L. minor or L. japonica accessions did. For an outdoor system that has to survive a winter, that difference is a design input, not a botanical curiosity.
For the step-by-step key, from root count to vein count to DNA barcode, see the companion guide to duckweed species identification. This page is the roster; that one is the method.
What this means if you are choosing or citing a Lemna species
Three practical consequences follow from a genus whose boundaries are still moving.
Treat the species name as a hypothesis until the material is genotyped. With more than a quarter of section Lemna clones misassigned in a major collection, a name on a culture tube or in a methods section is a claim, not a fact. Ask how the identity was confirmed and with which marker.
Choose the clone, not just the species. Within one species, growth and composition vary widely by isolate and by conditions, which is why the ranking of the fastest growing duckweed species changes from study to study. A species name narrows the field; it does not specify the plant.
Check which taxon a standard actually assumes. Regulatory toxicity work such as the OECD Lemna test is written around L. minor and L. gibba, the two species whose boundary the L. x mediterranea work has just blurred. A result is only as transferable as the identity of the plant behind it.
This is also where SERAPH’s own work sits. SERAPH Vision already distinguishes duckweed species on a real cultivation tray, frame by frame, because a canopy that drifts from one species to another changes what the system is measuring. We are early, and we say so: the system is at proof of concept, and outdoor field validation is still ahead. But the starting principle does not depend on maturity. The identity of the material is part of the measurement.
FAQ
Is Lemna the same as duckweed?
Lemna is one genus of duckweed, the original one named by Linnaeus. Duckweed as a group also covers Spirodela, Landoltia, Wolffiella and Wolffia. Every Lemna is a duckweed; not every duckweed is a Lemna.
What is the most common Lemna species?
Lemna minor, common duckweed, is the most widely reported. Many records of it turn out to be L. turionifera or the hybrid L. x japonica on closer inspection, so it is probably less dominant than the records suggest.
Is Lemna paucicostata a valid species?
No. It is an older name for Lemna aequinoctialis and should be cited under that name, although it still turns up in recent papers and culture catalogues.
Are Lemna japonica and Lemna mediterranea real species?
They are real plants, widespread and persistent, but they are hybrids rather than species in the usual sense. L. japonica comes from L. minor and L. turionifera; L. x mediterranea from L. minor and L. gibba. Both are written with an x to show their hybrid status.