Identifying Stigeoclonium species

'The genus Stigeoclonium includes all attached, branched, uniseriate, filamentous green algae of which the cells of the main axis and the branches are similar in size. The thallus is heterotrichous and made up of a prostrate and an erect system of filaments. The terminal cells of the erect filaments may produce multicellular, hyaline hairs. Both prostrate and erect cells may produce rhizoids...reproduction is predominantly asexual by means of quadriflagellate zoospores' (Francke and Simons, 1984).


Stigeoclonium plants growing on a slide exposed in a garden pond (June 2000). JK.

Stigeoclonium is well known for its phenotypic plasticity, in other words the growth form varies according to environmental conditions. This makes it extremely difficult to identify from field-collected material of the erect system, and as many as 40 'species' have been described at various times. The photograph above illustrates the different morphologies which can be found together.

Studies on cultured material has shown that the morphology of the basal (prostrate) system of filaments is a better guide to identification, and Cox and Bold (1966) were able to determine that 20 isolates contained only 7 species. Further work in The Netherlands reduced the species found there to 3 'groups', on the basis of the way that the zoospores develop after settlement (Francke and Simons, 1984; Simons et al., 1986).

These groups are:

Stigeoclonium helveticum

Stigeoclonium tenue

Stigeoclonium farctum

Here are some pictures of cultured Stigeoclonium, compared with field specimens


John Kinross

Page updated 27/2/12