Biology  Morphology 
Dimensions
  Not greater than 1 cm, the smallest sizes in Wolffia, from 2-5 mm..

Forms
  Of 30 species, 5 are encountered in Russia:
Morphological structure - vegetative body - listets or fronds. 
  The form of fronds can be reniform, rounded, eliptical, lancate, linear, or oval. 

Life cycle
  Plants are long-lived and overwinter rarely as seeds, more commonly they overwinter in the form of fronds.  Sometimes the fronds become thickened, more rounded and fill up with starch.  Such formations call turions or "quiescent kidneys."  They are encountered in Spirodela.  In autumn turions submerge to the bottom of the reservoir, and then in the spring they float up and begin to multiply further. (Pashkovich E, Yudin B.S., 1978)

Duckweed and the Snail
 
Lemna trisulca. It is interesting that this small-sized plant - widespread to abundant - is never attacked by snails.  This is because of prickly crystals of calcium oxalate, which are contained in its cells.  Fearing these crystals, snails do not touch it.(Zolotnitskiy N.F., 1993). 

V.I. Vernadskiy and duckweeds
On the chemical elementary composition of duckweeds (Lemna) as a species characteristic
 
In this work, Vernadskiy studies four duckweeds:  Lemna minor, Lemna polyrrhiza, Lemna gibba, Lemna trisulca. It was established that in the species, which grow in different geographical zones, can vary in their chemical composition.  For the experiment the
duckweeds, which grow in Kiev region and Peterhof region, were studied. Fourteen elements were investigated:
Н2О, C, N, H, O, K, Na, Ca, Mg, Mn, Fe, Cl, P, S, Si. It
It was established that the chemical composition for the separate species of duckweeds differed little depending on the locality or terrain.  Identifiable differences in chemical composition are specific to the different species of duckweeds. 

On the position of chloroplasts in ivy-leaf duckweed
  Ivy-leaf duckweed can change the color of its fronds.  In indirect or scattered light chloroplasts are arranged along the walls of the cells, on surface of which the light/world falls at a right angle, i.e., in the cylindrical parenchyma cells of the leaf on the parallel surfacesto the leaf surface, and therefore, the tissue of such cells seems dark green, if we look on them from the side, whence light/world falls. 

As soon as direct sunlight begins to have its effect, chloroplasts are transferred to the walls of cells, in parallel to the direction of the incident rays/beams.  If these are parenchyma cells, then chloroplasts are grouped on long side walls, while short and lying/horizontal the right angle to incident light walls prove to be those deprived of chlorophyll and without pigmentation. 
 

One can see well this displacement especially well in ivy-leaf duckweed, whose simple tissues contain only two layers of short green cells. 
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Краснодар, 2002