Sea lettuce ( Ulva lactuca )

The Ulvophyceae are a class of algae that belongs to the Chlorophyta, one of two major groups of green algae. Known representatives of sea lettuce and the model organism Acetabularia.


The representatives are unicellular ( kokkal ), or form unbranched or branched thalli. The most common form are unbranched filaments that grow by disordered cell division ( filamentous organization level). In Monostrema come by longitudinal division of the cells also scale structures. A sheet-like bilayer Gewebethallus forms of sea lettuce. The thallus is often multicellular ( siphonocladal ).

Floating cells possess one or two pairs of flagella without mastigonema. The basal bodies have four microtubule roots in a cross shape, and small roots in two different sizes, alternating between two or more microtubules. The flagella are covered with scales and have a Rhizoplasten.

The cell wall contains polysaccharides and is more or less calcified. Plasmodesmata are missing. Cell division occurs by constriction with a closed, centric and persistent mitotic spindle. A Phycoplast does not occur during cell division.

The life cycle is diplobiontisch, so there is a free-living gametophyte and sporophyte. These two phases can uniformly ( isomorphic ) or different ( heteromorphic ) be. Other green algae groups have mainly a haplobiontischen cycle.


The majority of species live in the sea water.


The class may not be monophyletic. There is no clear synapomorphies. There are no adequate genetic studies to clarify the question clearly. There are five clearly distinct groups, which are usually classified as orders:

  • Ulotrichales
  • Ulvales
  • Cladophorales (including Siphonocladales )
  • Caulerpales
  • Dasycladales