Calothrix [C.Agardh] Bornet & Flahault   

Kingdom: Eubacteria
Phylum: Cyanobacteria – blue-green algae
Order: Nostocales

British distribution (genus): Evidently widespread, freshwater and marine.
World distribution (genus): Cosmopolitan?

Calothrix, photomicrograph
Calothrix trichomes: material in culture, named as C. viguieri

Calothrix is characterised by its tapering trichomes with terminal (and sometimes intercalary) heterocysts [or 'heterocytes']. The lower part of the trichome is usually enclosed in a firm, colourless or yellow-brown sheath (not clearly visible in the cultured material shown here). The genus merges into the closely related genus, Dichothrix, distinguished by usually multiple trichomes within a single sheath and a greater tendency to 'false-branching'.

There are a number of species, some freshwater, others marine, forming thin, mucilaginous films or crusts on rocks and aquatic plants, including seaweeds. Calothrix also occus as a lichen photobiont, when it may become more or less unicellular or form short chains of globose cells rather than forming trichomes.

Calothrix or Dichothrix as lichen photobiont, photomicrograph
Photobiont in the maritime lichen, Lichina confinis. This is either Calothrix or possibly the very closely related genus Dichothrix. Material from maritime rocks, Arbroath, Angus, April 2002.

© A.J. Silverside
Page first hosted at, October 1998, revised January 2003; transferred to with minor edits, October 2009, last modified January 2010.
For text layout and clarity it is best viewed with Internet Explorer
Return to main Index
Conditions of Use home page