Floristische Werkgroep (FWE) Afdeling
Eindhoven
KNNV-logo
How to recognise the various Lemnoidae, such as Lemna, Wolffia, Spirodela
and other small floating plants such as Azolla, Ricciocarpos and Salvinia in the Netherlands.
By: Wim van der Ven
Aangepast:
Vlag_NL
Voor Nederlands
 Introduction Lemnoidae* and other small floating plants
*The duckweeds used to be classified as a family: the Lemnaceae. Presently they are classified as Lemnoidae, a sub-family of the Araceae.
      What can be found here:
In recent years I have been looking a lot at plants in the Lemnoidae, and at other small floating plants. The species discussed here I have in culture at home. A few species hibernate indoors. On this webpage I want to share my experiences, hoping to spread the knowledge about the small floating plants.

      Notes:
This page is not finished. There are still pictures to be added and texts to be adjusted. I hope the reader will pass on improvements and remarks to me. This can improve the data.
Thanks in advance.
wimvdven@freedom.nl

      Explanation:
You can scroll through this page. But you can also go to a species directly by clicking a species in the top menu.
Most pictures can be enlarged by clicking them. The pictures will be displayed in a new window. You can return by closing that window.



On 3 May 2007 I took this photo of part of the pond near the crematorium on the Maeterlinckweg in Rotterdam.
On display are:
The largest fronds: Spirodela polyrhiza
The smaller fronds: Lemna turionifera
The smallest plants are: Wolffia's plants.
At the time I called these the Wolffia's plants Wolffia arrhiza
That turned out to be wrong. It is Wolffia columbiana.
This picture is the oldest record of Wolffia columbiana in the Netherlands.

Plaatje

 Lemna L. Menu 
All Lemna species have one root per frond. Often several fronds are joined. Reproduction is mainly vegetative. Daughter fronds emerge from the two lateral slits. Later these daughter fronds form new daughters again. We call them ‘daughters', but that is actually not correct. The Lemna species can flower. The flowers are unisexual, monoecious, without an perianth; the inflorescence consists of one female and two male flowers. However, some authors consider the inflorescence as one bisexual flower 1.
An important feature is the number of veins. Unfortunately, these are not always easily visible.
1(Bron: S. J. van Ooststroom, TH. J. Reichgelt, Flora Neerlandica, deel I, aflevering 6.

 
Plaatje Plaatje Plaatje
Lemna minuta, Lemna minor and Lemna gibba in the field.
Explanation of different components of Lemna species
Lemna minuta (with flowers) and Lemna gibba

 Lemna aequinoctialis Welw.   Menu 
There are two Lemna-species with a wing at the root sheath: Lemna perpusilla and Lemna aequinoctialis. The main difference between the two is the number of ribs on the seed. I think my material here in the pictures is Lemna aequinoctialis, for the following reasons. .
Difference
Lemna perpusillaLemna aequinoctialis
ovate-obovateovate-lanceolate *
1-4 mm1-6 mm
1-1.7 times as long as wide1-3 times as long as wide *
Seeds with 35--70 indistinct ribs, staying within fruit wall after ripening.Seeds with 8--26 distinct ribs, falling out of fruit wall after ripening
1 distinct papilla near apex on dorsal side, 2--3 very distinct papillae above node1 often very distinct papilla near apex on dorsal side and 1 above node;*
sheath narrowly winged at base (wing 2--3 times as long as wide). sheath winged at base (wing 1--2.5 times as long as wide) *
Table compiled from data from http://www.efloras.org
* is what I think applies to my material.

      Characteristics:
1 root, 3 veins on the dorsal side visible as elevations, length 1-6 mm, 1-3 times as long as wide. Root sheath winged, wing 1-2.5 times as long as wide. No red colour. Does not form turions.

      May be confused with:
At first sight with Lemna minor. Both have 3 veins. Lemna aequinoctialis has a more regular shape and a lighter colour.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna aequinoctialis in a 32 mm diameter tube. Here, at the dorsal side, the veins can be seen clearly.
 
Photo of Lemna aequinoctialis together with Salvinia natans made in the Victoria greenhouse in the botanical garden in Leiden (the Netherlands).
The winged root sheath. This can be seen by looking from the back to the front of the frond.
Plaatje Plaatje Plaatje
The winged root sheath. This can be seen by looking from the back to the front of the frond.
Schematic diagram of the wing (side view).
Schematic diagram of the wing (bottom view).

 Lemna gibba L. Menu 

      Characteristics:
1 root, veins (3-)4-5(-7), length 1-8 mm, 1-1.5 as long as wide, The fronds are often saddle-shaped, Plaatje i.e. a semicircle with a triangle towards the tip. At the ventral side are large cells which usually together form a swelling.
Lemna gibba can also have an asymmetrical appearance like Lemna minor.
The most striking feature is the large air cells at the ventral side of the plant making it thick.
Sometimes red at the dorsal side. This can be seen as red speckles at the surface.
In autumn the plants become smaller, turn to a grey-green colour and sink to the bottom.

      Special features:
Sometimes Lemna gibba is flat and can be confused with Lemna minor. This is the case in winter, but in other seasons it occurs also under unfavourable conditions.

      May be confused with:
Flat Lemna gibba can be confused with Lemna minor. But Lemna gibba is slightly larger, has a more regular shape and the cells on the ventral side are larger.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna gibba in a 32 mm diameter tube.
Lemna gibba makes a kind of turions. These have roots. The turions ofLemna turionifera and Spirodela polyrhiza have no roots.
Lemna gibba in Zuiderpark, The Hague. Sometimes the dorsal side is coloured red.
Plaatje    
The swellings can be seen. Sometimes Lemna gibba is flat.
 
 

 Lemna minor L. Menu 
The best-known duckweed is Lemna minor, which until a few years ago was most the common species in the Netherlands.

      Characteristics:
1 root, 3(-5) veins, size 1-8 mm, 1.3-2 times as long as wide. Asymmetrical, Plaatje i.e. one side is more round than the other one is. ventral side green. Sometimes the plants are red. The red colour is in the plant and not as in Lemna gibba where the red colour is in specks at the dorsal side.

      Special features:
The veins are not always visible, especially in the field. Sometimes you can see them with a hand lense by holding the plant up to the sunlight. It may be possible to make the veins visible by putting the plants in alcohol , e.g. methylated spirit, for a few hours. The veins decolour later than the rest of the frond. These methods also apply to the other species in this genus.

      May be confused with:
Sometimes Lemna gibba is flat and looks a lot like Lemna minor, but Lemna minor is asymmetric and has smaller air cells.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna minor in a 32 mm diameter tube.
The asymmetrical sides are clearly visible here.
Lemna minor in the field.
After the fronds have been left in the alcohol for a short time, you can see the three veins.
Plaatje    
I once found Lemna minor flowering.
 
 

 Lemna minuta Kunth Menu 
Lemna minuta has overtaken Lemna minor in distribution in the last decade. Seemingly, Lemna minuta has in recent years become more common than Lemna minor.

      Characteristics:
1 root, 1 vein, length 0.8 -4 mm, 1-2 times as long as wide,
The shape is elliptical, the sides are more or less parallel. Plaatje
Grows well in the shade, with a lot of light the plant becomes light in colour, almost transparent. Lemna minuta is the most frost resistant of all Lemna species. A Lemna blanket in winter is almost always Lemna minuta.


      May be confused with:
When Lemna minor is very small, it may look like Lemna minuta. But usually Lemna minuta regular in shape.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna minuta in a 32 mm diameter tube. In the field it usually looks like this.
Lemna minuta in a 32 mm diameter tube. Sometimes the fronds are very thin.
Lemna minuta in the field.
Plaatje Plaatje Plaatje
Lemna minuta with flowers. The white dots are the anthers.
Lemna minuta is sometimes transparent, making it look like a different species. This is possible if they get very much light. The vein is clearly visible in this photo.
Lemna minuta with one vein

 Lemna trisulca L. Menu 

      Characteristics:
1 root (sometimes not developed), (1 or) 3 veins, 3-15 mm, 2-3.5 times longer than wide.
4-10 mm long
Unlike the other duckweeds, Lemna trisulca is not roundish but elongated with a point at the end. Branching is more or less crosswise. Plaatje
While the other duckweed plants float at the surface, Lemna trisulca floats submerged. When it flowers, the differently shaped fronds float at the surface.

      Special features:
Very rarely flowering in the Netherlands. The shape of the flowering fronds is more or less square. They are thicker than the vegetative plants and no longer transparent.

      May be confused with:
Lemna trisulca can hardly be confused with another Lemna.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna trisulca in a 32 mm diameter tube.
The shape of the flowering plants at the surface is square rather than roundish.
I have yet to investigate whether flowering Lemna trisulca does have roots always.
Flowering Lemna trisulca
Plaatje Plaatje  
Lemna trisulca floating under the surface
Here the veins can be seen clearly.
 

 Lemna turionifera L. Menu 
Lemna turionifera is only a few decades in the Netherlands. Or have we overlooked it previously?

      Characteristics:
1 root, 3 veins, length 1-4 mm, 1-1.5 times as long as wide,
The shape is between Lemna minor and Lemna gibba in, but symmetrical. Plaatje Plaatje
An important feature is that this species turns red at the ventral side. This colouring starts at the root attachment. This colouration causes the dorsal side to look grey. The size is between Lemna minor and Lemna minuta.
Just like Spirodela polyrhiza Lemna turionifera produces turions, winter buds. These are small, grey-green fronds without roots which sink to the bottom to hibernate. When conditions are favourable again, the turions surface and new plants grow from them.

      Special features:
Depending on the growing conditions the intensity of red colour at the ventral side varies from intensly red to hardly visible.

      May be confused with:
Lemna minor because it has 3 veins, but Lemna turionifera is symmetrical and is red, starting at the root.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Lemna turionifera in a 32 mm diameter tube. The reddish colour is clearly visible here.
Here you can see the red colour at the ventral side around the root.
At the left turions of Lemna turionifera and at the right of Spirodela polyrhiza

 Lemna valdiviana Phil. Menu 
This species is still being worked on.

      Characteristics:
1 root, 1 vein, length 1-5 mm, 1.3-3 times as long as wide; asymmetrical, one side almost straight, the other side convex.

      Special features:
...


      May be confused with:
...

Plaatje Plaatje  
Lemna valdivianain a 32 mm diameter tube.
The fronds of Lemna valdiviana face each other two by two, making them look star-like.
 

 Spirodela Schleid. Menu 
 

      Characteristics:
 

      Special features:
 

      May be confused with:
 
 
 
  
 
 
 
 
 

 Spirodela polyrhiza (L.) Schleid. Menu 
 

      Characteristics:
Spirodela polyrhiza and S. punctata are the only duckweeds with more than 1 root. Spirodela is the largest of the duckweeds and as long as 3-10 mm.
The shape is round-ovoid. Length:width = 1.2:1 Plaatje. The plants have 5 or more veins. The ventral side is red. Only one root pierces the scale at the ventral side of the plant.

      Special features:
In autumn, Spirodela polyrhiza forms winter buds without roots, gray-green in colour and smaller than the parent plant. These winter buds, also called turions, sink to the bottom and surface in spring, growing out to their normal form.

      May be confused with:
Spirodela punctata because it also has more than 1 roots. But Spirodela polyrhiza is comparatively much more circular(length : width = 1.2:1)
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Spirodela polyrhiza in a 32 mm diameter tube.
 
This photo shows both the dorsal side and ventral side.
In the photo several veins can be seen.
Plaatje Plaatje  
Sometimes the ventral side is gibbous as in Lemna gibba
At the left turions of Lemna turionifera and at the right of Spirodela polyrhiza
 

 Spirodela punctata(G. Mey.) C.H.Thomps Menu 
Syn. Landoltia punctata Les & D.J. Crawford

      Characteristics:
(1-)2-7(-12) roots, (3-)5-7 veins, length 1.5-8 mm, 1.5-2 times as long as wide.
Red/purple on the ventral side. All roots pierce the scale at the ventral side of the plant.

      Special features:
This species is not native yet, but he is found in garden centres or in ponds with plants which originate from a garden centre.
The The NVWA (Dutch Food and Consumer Product Safety Authority) considers this species to be an invasive aquatic species. See, as Landoltia punctata in the chapter Links "Herkennen en bestrijden invasieve waterplanten" (in Dutch).

      May be confused with:
Because Spirodela punctata has multiple roots and a red ventral side, this species can be confused with Spirodela polyrhiza, but S. punctata is 1.5-2 times longer than wide, whereas in Spirodela polyrhiza this ratio is 1-1.5 times. Also Lemna turionifera has a red ventral side, but this one has only one root and the colouration starts at the root attachment.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Spirodela punctata in a 32 mm diameter tube.
Spirodela punctata.
Spirodela punctata seen from above. You can clearly see the red edge, which is different from Spirodela polyrhiza who has less of it.
multiple roots    
Spirodela punctata seen from below. This ventral side is red. A similarity to Spirodela polyrhiza
Here you can also see the multiple roots.

 Wolffia Schleid. Menu 
Until 2014 Wolffia arrhiza was the smallest flowering plant in Europe. It has never flowered here.
Before, recording was easy. If one saw a small globose plant without a root Wolffia arrhiza was recorded. Nowadays in the Netherlands we have three Wolffia species and one more is expected.
All Wolffia plants do not have flat fronds, like the Duckweeds, but they are globose.

At the right are the explanations of the terms used on this web page. First, the distinction between front and back. The front is the side where the young plants emerge. The other side is what I call the back. The length and width are to be seen in top view. The distance between the front and back is called the length. The width is the distance between the two sides, perpendicular to the length. The depth is the distance between the dorsal side and the bottom of the plant.

      Characteristics:
Plants without roots, more or less globose. At the front a young plant (daughter) always appears. Before this one leaves the mother plant, the next daughter is developing already..

      Special features:
I think everything about these plants is quite special.

      May be confused with:
Sometimes Lemna plants of which roots have rotted away are incorrectly called Wolffia. But Lemna plants have flat fronds while a Wolffia is globose. A Lemna root which has rotted away, always leaves a mark at the place of attachment.
Plaatje
Uitleg rand    
The edge is the darker outer rim contrasting with the brighter inner part.
 
 

 Wolffia arrhiza (L.) Horkel ex Wimm. Menu 
In side view the upper part the body is coloured slightly more intensely than at the rest. This is caused by the fact that the upper part has more and smaller cells than the rest.

      Characteristics:
Number of roots 0, Number of veins 0.
Plants floating at the surface. Spherical. In top view bright green.
This plant is only 0.6 to 1 mm in size.
In top view a small part of the underwater growing body can be seen as an lighter coloured edge.
More than 75% of the dorsal side protrudes above the water surface.
On the dorsal side an elevation can be seen at the back.

      Special features:
The distribution map also shows the observations including Wolffia columbiana. Until the discovery of Wolffia columbiana in 2014 all Wolffia plants were recorded as Wolffia arrhiza. But in retrospect we know that Wolffia columbiana was already present in the Netherlands in 2006, perhaps even earlier.
My first observation of Wolffia columbiana is in Leiden, in the Doelengracht which runs through the Hortus Botanicus. I had taken a photo here on 2 June 2006. Recently I looked closely at this photo and then I saw it is Wolffia columbiana.

      May be confused with:
The other Wolffia species.
Plaatje
Click the image for the distribution atlas
(in a new window)

Plaatje Plaatje Plaatje
Wolffia arrhiza in a 32 mm diameter tube.
Side view:
The cells just below the surface are slightly smaller than the lower ones. As a result, the cells just below the surface a coloured more intensly than the lower ones. Here you can also see Wolffia arrhiza is not entirely spherical. You can also see the elevation at the back.
Top view:
In top view the body is barely visible, It is only a small edge.
I find Wolffia arrhiza in top view is turtle shaped, with a pointed back

 Wolffia australiana (Benth.) Hartog & Plas Menu 
The first record of Wolffia australiana was in Berkel en Rodenrijs by Bureau Waardenburg in 2014.

      Characteristics:
Wolffia australiana is much deeper than the other two Wolffia species: 2-3 times as deep as wide.
The top has a bright green colour. In top view the rest of the body cannot be seen, in other words there is no edge.
This Wolffia is somewhat smaller than Wolffia arrhiza and Wolffia columbiana, especially much narrower, length 0.5-0.7 mm.

      Special features:
Until now Wolffia australiana is found in a few places only. Considering how it behaves in my breeding buckets, I expect the species will start to behave invasively.

      May be confused with:
At first glance with the other Wolffia species, but this one is much deeper than the other ones and in top view the rest of the body is not visible (no edge).
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Wolffia australiana in a 32 mm diameter tube.
Some Wolffia australiana in a 32 mm diameter tube. There are a few Wolffia columbiana among them
Side view:
The cells just below the surface are slightly smaller than the lower ones. As a result, the cells just below the surface a coloured more intensely than the lower ones. These cells just below the surface are smaller and coloured more intensely than those of the other Wolffia species. The depth of this Wolffia is longer than the width.
Plaatje    
Top view:
Intense green colour. No parts of the body visible. I don't know if those speckles are stomata.
 
 

 Wolffia columbiana H. Karst. Menu 
Nowadays, a few years after the discovery, Wolffia colombiana is being found in many more places, also outside the western Netherlands. It seems that by now Wolffia columbiana is more common than Wolffia arrhiza is. In Rotterdam, where Wolffia arrhiza was noted previously, Wolffia columbiana is now the most common species

      Characteristics:
The length is about 0.6- 1.1 mm.
The surface is more convex than the flat surfaces of Wolffia arrhiza and Wolffia australiana. The cells just below the surface are only slightly smaller than the lower ones. As a result, in side view de plant is coloured rather uniformly.
Most part of the plant is submerged. In top view you can see a relatively large portion of the submerged part, so the edge is rather wide.

      Special features:
Wolffia columbiana was recognised only in 2014, but afterwards I saw on old photos it was present in 2006 already.

      May be confused with:
The other Wolffia's.
In Wolffia columbiana the ratio of width : depth is about 1 : 1, in Wolffia arrhiza 1 : 1.2 and in Wolffia australiana 1 : 2. The latter two are bright green at the dorsal side, while Wolffia columbiana is more or less transparent, so the colour is faint.
While Wolffia columbiana in side view is rather uniformly coloured, in Wolffia arrhiza and Wolffia australiana the cells just below the surface are coloured more intensely than the lower ones.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Wolffia columbiana in a 32 mm diameter tube.
Side view.
All cells are more or less transparent and uniformely coloured.
Top view:
The widest part (the edge), which is submerged, can easily be seen.

 Wolffia globosa (Roxb.) Hartog & Plas Menu 
Wolffia globosa has not yet been found in the Netherlands, but Bureau Waardenburg is expecting this species. The material I have, comes from the Hortus Botanicus in Leiden.

      Characteristics:
In top view Wolffia globosa is elliptical.
Length 0.4 - 0.6 mm.
Width : depth = 1 : 1.

      Special features:
Already seen among material from a botanical garden.

      May be confused with:
Wolffia columbiana. It has the same colours but the plants are smaller and narrower.
There is, obviously, no distribution map available yet.
Plaatje Plaatje  
Wolffia globosa in a 32 mm diameter tube.
More photos are planned.
 

 Azolla filiculoides Lam. Menu 

      Characteristics:
Plants 1-4 cm, sometimes larger. Leaves covering each other like roof-shingles (imbricate). They have a membranous margin.

      Special features:
The plants are green at higher temperatures and become brick-red under unfavourable conditions, e.g. when cold.
The NVWA (Dutch Food and Consumer Product Safety Authority) regards this species an invasive aquatic plant. See in the chapter Links "Herkennen en bestrijden invasieve waterplanten".
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Azolla filiculoides in a 32 mm diameter tube.
Sometimes you think you discovered a new cycle path, but it is a ditch with Azolla filiculoides.
Azolla filiculoides at closer look.
Plaatje Plaatje  
The plant is made up of small leaves arranged like roof shingles.
Roots originate at several places.
 

 Ricciocarpos natans (L.) Corda Menu 

      Characteristics:
Seemingly, the plants do not lie against each other as Lemna plants do, because the ventral rhizoides grow wider than the thallus, determining the distance between the plants.

      Special features:
Ricciocarpos natans is not a vascular plant, it is a liverwort. The reason I include it here, is that it is also a small, floating plant which you may encounter in the field.

Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Ricciocarpos natans in a 32 mm diameter tube.
Top view.
The rhizoides at the ventral side.

 Salvinia adnata Desv. Menu 
An often used synonym is Salvinia molesta D.S. Mitch.

      Characteristics:
Branches with three leaves each in a whorl. Two leaves float and the third leaf acts as a root. A number of these whorls form branches. Side branches detach after a while and continue to grow independently. The floating leaves are about 1.5 - 2 cm long.
The hairs on the papillae are fused at the top. .

      Special features:
The hairs on the papillae repel water.
Actually, the species is only found because the plants are discarded from aquaria. Usually they do not hibernate.
The NVWA (Dutch Food and Consumer Product Safety Authority) regards this species an invasive aquatic plant. See in the chapter Links "Herkennen en bestrijden invasieve waterplanten".

      May be confused with:
Salvinia molesta of which the hairs on the papillae do not touch each other at the top.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Salvinia adnata in a 32 mm diameter tube.
 
A branch.
Rootlike submerged leaves.
Plaatje    
The touching hairs on the papillae.
 
 

 Salvinia natans (L) All. Menu 

      Characteristics:
Branches with three leaves in a whorl. Two leaves float and the third leaf acts as a root. A number of these whorls form branches. Side branches detach after a while and continue to grow independently. The floating leaves are about 1 - 1,5 cm long.
The hairs on the papillae are separate at the top.

      Special features:
The hairs on the papillae repel water.
Actually, the species is only found because the plants are discarded from aquaria. Usually they do not hibernate.

      May be confused with:
Salvinia adnata whose hairs on the papillae are fused together at the top.
Plaatje
Click the image for the distribution atlas
(in a new window)
Plaatje Plaatje Plaatje
Salvinia natans in a 32 mm diameter tube.
 
Part of a branch with a drop of water on a leaf.
Rootlike submerged leaves.
Plaatje    
The spreading hairs on the papillae.
 
 

The pictures can be enlarged by clicking them. The pictures will be displayed in a new window. You can return by closing that window.
 Key  Menu 
1 Plants without roots. (Note: When a root has rotted away from the frond, the root attachment can still be seen.) Plaatje → 2
- Plants with one or more roots. Plaatje → 8
2
(1)
Plants more or less spherical (Wolffia). Plaatje → 4
- Plants are flat fronds. Plaatje → 3
3
(2)
Plants olive green and more or less elliptical. Plaatje → 7
- Plants green and more or less triangular or quadrangular1. Plaatje Lemna trisulca
4
(2)
The largest width above water. In top view the submerged part is invisible (no edge). Top view uniformely bright green. Plaatje Wolffia australiana
- The largest width is submerged, in top view you can see a large part of the submerged plant, the edge. The width of the edge is 10 to 50 % of half the diameter.
(note: the edge is the darker outer rim contrasting with the brighter inner part. See explanation of the edge at Wolffia)
Plaatje → 5
5
(4)
The edge is about 10 - 25 % of half the diameter. Plaatje Wolffia arrhiza
- The edge is 25 - 50 % of half the diameter. Plaatje → 6
6
(5)
The plant is about as wide as it is long. Plaatje Wolffia columbiana
- Plant is about twice as long as wide. Plaatje Wolffia globosa
7
(3)
Fronds 1 x 2 mm, elliptical, turions of Lemna turionifera (at the left side of the photo) Plaatje Lemna turionifera
- Fronds 2 x 3 mm, kidney-shaped, turions of Spirodela polyrhiza (at the right side of the photo ) Plaatje Spirodela polyrhiza
8
(1)
Fronds with 1 root (Lemna). Plaatje → 10
- Fronds with more than 1 root. Plaatje → 9
9
(8)
Fronds flat, without hairs. Plaatje → 17
- Leaves concave or leaves with hairs. Plaatje → 18
10
(8)
Plants submerged. Frond long, usually longer than 1 cm, a number of them attached to each other. Plaatje Lemna trisulca
- Plants float at the surface, fronds smaller than 1 cm. Plaatje → 11
11
(10)
Plants more or less triangular or quadrangular1. Flowering Lemna trisulca. Plaatje Lemna trisulca
- Plants more or less elliptical. Plaatje → 12
12
(11)
Fronds slightly thickened or with distinct swellings, saddle-shaped, air cells larger than 0.3 mm. Plaatje Lemna gibba
- Fronds flat, more or less elliptical, air cells smaller than 0.3 mm. Plaatje → 13
13
(12)
Ventral side of the fronds is red, starting at the root. Plaatje Lemna turionifera
- Ventral side green. Plaatje → 14
14
(13)
Shape of fronds irregular, one side is more curved than the other one is. Plaatje → 15
- Shape the fronds regularly, both sides equally curved or straight. Plaatje → 16
15
(14)
Sides unevenly curved, 3 veins. Plaatje Lemna minor
- One side almost straight the other one curved, 1 vein. Plaatje Lemna valdiviana (?)
16
(14)
In top view vein not visible as an elevation, length 0.8-4 mm. Plaatje Lemna minuta
- In top vieuw vein visible as an elevation, length 1-6 mm, root sheath winged. Plaatje Lemna aequinoctialis
17
(9)
Fronds about as wide as long, almost round. Plaatje Spirodela polyrhiza
- Fronds distinctly longer than wide, in top view with a red margin. Plaatje Spirodela punctata
18
(9)
Leaves elliptical with water-repellent hairs. (Salvinia) Plaatje → 19
- Leaves two-lobed or with scale-like leaves arranged like roof shingles. Plaatje → 20
19
(18)
Hairs on the papillae touching each other at the top. Plaatje Salvinia molesta
- Hairs on the papillae not touching at the top. Plaatje Salvinia natans
20
(18)
Leaves scale-like, arranged like roof shingles. Plaatje Azolla filiculoides)
- Plants 2-lobed. Plaatje Ricciocarpos natans
1 I don't know whether flowering Lemna trisulca does have a root or not. I think both occur.




 Further Information   Menu 
 
 Sending material   Menu 

If you want to send material:
(Please, first mail whether I am at home).

Put the material in damp kitchen paper. (Not wet because this will leak. Soak it first and squeeze it.)
Put that in a waterproof plastic bag in an envelope, along with name, the location (preferably with coordinates), date and your e-mail address to:

Wim van der Ven
Ridderzaal 116
5653 RE Eindhoven
The netherlands

You can also contact me anytime for information by sending an email:
wimvdven@freedom.nl
 
 Justification  Menu 

Photos and drawings: Wim van der Ven.

At this point, I would like to thank John Bruinsma.
He has always inspired and encouraged me to get involved with the duckweeds and to share the information I gained in the process with others. He also provided me with material collected abroad.

Pijl naar links
 Links  Menu 

I consulted the links below. They will open in a new window.

Wayne P. Armstrong
A comprehensive site with very much information on Lemnoidae.

Direct link to the key in the previous site

efloras, Flora of North America, Wolffia
Electronic Wolffia key of North America.

efloras, Flora of North America, Lemna
Electronic Lemnas Key of North America.

Bureau Waardenburg
Employees of this office discovered Wolffia columbiana and Wolffia australiana in the Netherlands (in Dutch).

NDFF Verspreidingsatlas Vaatplanten
This contains the distribution pictures of all species found in the Netherlands, with photos and a description (in Dutch).

The Plant List — A list of all plant species
In this site all plant names are listed with the note whether that name is recognized or a synonym.

Ulf Schmitz, Steffen Köhler & Hasko Nesemann (pdf)
On the discovery of Wolffia columbiana and its distribution in Europe.(In German, with an abstract in English)

NVWA Herkennen en bestrijden invasieve waterplanten
The field guide 'Invasieve waterplanten in Nederland' can be downloaded here. (In Dutch)

Boekenkast This Bookcase on the Mimosastraat in Utrecht was painted by JanIsDeMan.
 Literature  Menu 

Books

  • S. J. Van Ooststroom, TH. J. Reichgelt, ea. 1964. Flora Neerlandica, deel I, aflevering 6
  • Van der Meijden, Ruud (2005). Heukels' Flora van Nederland. 23e druk, Wolters-Noordhoff, Groningen.
  • Joep Spronk, John Bruinsma & Fred Lambert (2006). Atlas van de flora van Eindhoven. Ontwikkeling van de flora in de regio in de twintigste eeuw. KNNV afd. Eindhoven, Eindhoven
  • E.J. Weeda. Nederlandse oecologische Flora, Wilde planten en hun relaties deel 1 en 5.
  • J. Mennema. Geïllustreerde Flora Van Nederland 23ste editie; Heimans Heinsius Thijsse.
  • Klaus van de Weyer. Bestimmungsschüssel für die Makrophyten (....) in Deutschland Band 1: Bestimmungsschlüssel.
  • Klaus van de Weyer. Bestimmungsschüssel für die Makrophyten (....) in Deutschland Band 2: Abbildungen.
  • Rothmaler. Exkursionsflora von Deutschland 3, 11. Auflage 2007
  • Rothmaler. Exkursionsflora von Deutschland 4, 10. Auflage 2005

Magazines, yearbooks

  • Buxbaumiella 105 (2016). Op zoek naar kroosmos. Aquatische en terrestrische standplaatsen van Ricciocarpos natans in het rivierengebied. Gerben van Geest & Jurgen Nieuwkoop (In Dutch, with an abstract in English)
  • Gorteria, vol 2 (1964) nr. 6 p. 68-72 Over de oecologie van bloeiende Lemna trisulca. C. den Hartog (In Dutch, with a summary in English)