Nostoc commune, a remarkable terrestrial "blue-green alga"
Hilary Belcher Ph.D., D.Sc., 23 Pepys Way, Girton, Cambridge CB3 OPA
At the end of February this year Martin Heywood of this Club sent me an object
resembling a roughly circular wrinkled lump of brown jelly, which, together with
others of the kind, occurred along a track near Skreens Wood, Roxwell, Chelmsford,
NGR TL622093. This was a colony of Nostoc commune (Linnaeus) Vaucher ex
Bornet et Flahault. It belongs to a group of organisms that used to be known as the
blue-green algae or Cyanophyta, but is now called the Cyanobacteria, because its
members have more in common in biochemistry and fine structure with the bacteria
than with any group of algae.
Figure 1A, Martin Heywood's specimen of Nostoc; IB, filaments in a gelatinous matrix
from the interior of a colony.
The colonies of Nostoc are composed of numerous filaments of small cells in a
gelatinous matrix (see figure). During dry weather the whole colony shrivels to a flat
dark mass resembling a dead leaf or merely a dark stain on the earth or stones, but
after one or two rainy days it swells up to its original size.
This apparent sudden manifestation drew attention to it in medieval times and later,
and a large amount of speculation and folklore developed about it, mainly in the 17th
century, but persisting until recently in some parts of the country. The generic name
Nostoc, of unknown derivation, was given to this mysterious object by the early 16th
century chemist Paracelsus. In particular, Nostoc, mainly N. commune, was thought to
be the wreckage of a fallen star. Thus Martin Ruland, a 17th century alchemist, wrote
"Nostoch - a Ray or Radiation of a certain Star, or its offscouring, superfluity, etc.,
cast on earth. It falls, chiefly during June, July and August, upon broad fields or
meadows, being like a large fungus or sponge in appearance, and of a yellow or dark
Essex Field Club Newsletter No. 33, September 2000
11