In Osmundea pinnatifida gametophytic and tetrasporophytic plants can be dis
tinguished on the basis of the different DNA content of nuclei in cortical
and outer medullary cells obtained from subapical parts of the thallus. No
significant differences exist between the two life cycle phases in the DNA
content of nuclei of epidermal cells and medullary cells with 10 or more nu
clei. Mixed phase thalli producing spermatangia and tetrasporangia have DNA
contents in cells with 2-9 nuclei that correspond to gametophytic plants.
In central and basal parts of the thallus, cortical and medullary cells of
gametophytic and mixed phase thalli attain nuclear DNA content values simil
ar to those in the respective tetrasporophytic cells. 1C nuclei contain abo
ut 0.23 pg DNA.