Cyanobacteria (cyanophyta, cyanophytes)*,
commonly known as blue-green algae and as an occasional nuisance in
lakes and pools, "are arguably the most successful group of
microorganisms on earth" , which even have brought forth true
multicellular species  in the sense that their cell plasma is
interconnected. They do not store their genetic material
in a nucleus: a primitive trait which they have in common with bacteria
and the less well known but likewise numerous species of archaea. The
lack of a nucleus controlling the processes of life in the cells is
considered so essential that the blue-green algae are placed far apart
from the green algae, other algae, fungi, land plants, and animals on
the Tree of Life which represents the descent of the organisms.
it is all the more fascinating to see that the lowly beings which seem
come up to us right from the dawn of life on Earth can stick to each
other to form filaments and can form tufts of filaments into wondrous
shapes as if mimicking higher life forms. Although this is not typical
it is worth mentioning since it may draw
attention to the fact that fossil evidence of these organisms is not
restricted to bulky stromatolites or Ám-size unicells but can
occasionally show up as cm-size objects as seen here. Perhaps
the leaf-like formations serve the same purpose as real leaves do:
easier access to sunlight and solutes, compared to configurations with
all cells in a globular lump.
Generally it can be said that
well-preserved cyanobacteria, also
inconspicuous ones, seem to be rare fossils .
Fossil filamentous cyanobacteria grown in tufts on submerged and
decayed land plants and trimmed into pointed shapes by means unknown.
Rhynie chert, Lower Devonian.
Heights of the pictures:
7mm (left), 11mm (right)
Chert News 56
Chert News 67
Chert News 68
Chert News 71
Chert News 80
* These terms are usually regarded as synonyms.
I. Stewart, I.R. Falconer: Cyanobacteria and
cyanobacterial toxins, in: Oceans and human health,
P.J. Walsh, S.L. Smith, L.E. Fleming, Academic Press 2008,
E. Schirrmeister, A. Antonelli, H.C. Bagheri:
The origin of multicellularity in cyanobacteria.
BMC Evolutionary Biology 2011, 11:45
 T.N. Taylor,
E.L. Taylor, M. Krings: Paleobotany,
Elsevier 2009, 115-117.