The genus Stigeoclonium was established by Kuetzing in 1843 with five species which were originally described under Conferva and Draparnaldia. Later, Kuetzing (1845, 1847, 1849) transferred more species from Draparnaldia, added several new species and varieties, and again in 1853 he added, transferred and rearranged different species and varieties, some of which might be regarded now as simply ecological variations. More than one hundred years have passed since Kuetzing’s original publications. During this time many other new species have been described and others have been transferred to the genus from Draparnaldia (cf. Schmidle, 1900), from Endoclonium (cf. Hansgirg, 1898, Heering, 1914), and from Pseudochaete (Tiffany, 1937). On the other hand, some Stigeoclonium species have been transferred to another genus Cloniophora (Bourrelly, 1952). This indicates that there must be some confusions and uncertainties in respect to the delimitations of these genera. The present work was undertaken to:
(1) Critically investigate this matter as much as possible with the help of originally described specimens as well as other collections.
(2) Determine and delimit the generic level of the above genera which are closely related, especially Stigeorlonium, Cloniophora and Draparnaldia.
(3) Understand the polymorphic nature and range of variations of the species and to separate them on comparative basis. For this purpose large number of herbarium specimens and living plants have been studied.
(4) Bring together in one place all the relevant informations about the genus from the works on taxonomy, ecology and culture studies which are directly or indirectly related to our better understanding of the species-concept and probably a first venture to study large number of collections from different parts of the world with a view to revise and make a contribution towards the monograph of the genus Stigeoclonium. (5) Show the range of chloroplast structure, rhizoids, hairs, cell walls, life-cycles, zygospore structures and other vegetative and reproductive characters with a view of showng whether it is possible to combine some previously recognized taxa together and placed them in some small groups. This comparative study on. vegetative and reproductive structures may be elaborated further by future investigations to add to our knowledge of the affinities and differences between the species. This may also help to understand the general trend of morphological variations from simple to complex or advanced forms and to arrange them in a hypothetically phylogenetic series.
(6) Evaluate the true nature of the species of Stigcoclonium not in a traditional, orthodox and typological sense, but in a lieberal, non- conservative way in which values of ecological and cultural works have been considered in order to determine with unbiased and un- prejudiced mind “good species” from among manifold variations. In a monographic work, the student becomes a “lumper” or “splitter” or both, according to his definition of species. Some workers may be prejudiced beforehand as to the course of the work to be followed. Here, no preconceived idea was allowed to interfere with the decision taken afterwards. The facts were determined first, then the conclusion was derived. In some considerations I had to differentiate several varieties. Again, in some instances it was judged necessary to combine several species according to the facts exhibited by the type specimens and other collections. A limited number of drawings are included herein to maintain this principle and to show the range of variations. Illustrations of those species which are deemed invalid or doubtful have been included, for example, S.pygmaeum, S.polymorphum, S. autumnale, and S. weissianum. These specimens show striking similarities to one another and all of them show young stages of growth and could be assigned to a valid species if their full growth-form and life-histories were known from comparative cultural studies.
Although some cultures have been studied no attempts have been made to follow the entire life-cycle of any species, nor was it possible to get all species in living form from any source. It was impossible to collect and culture all the species from different parts of the world in the time available. It is assumed, however, that in the future, studies on life-history, cytology and morphological features mentioned above may reveal more about the ‘true’ nature of ‘species’ in this highly polymorphic group of plants.