Karyological investigatoins were made on 24 taxa of Spirogyra Link and their chromosome numbers have been reported. The chromosome numbers in various taxa exhibited a wide variation ranging from n=2 in S. VRG 80 to n=92±2 in S. nitida, the latter being the highest chromosome number recorded for any species of Spirogyra so far. S. minuticrassoidea is a new addition to Indian flora. A survey of the chromosome numbers in Spirogyra Link suggests that aneuploidy or agmatoploidy has played a more significant role than euploidy in its speciation. No correlations were observed between the width of filaments and/or number of chloroplasts per cell and chromosome numbers.
From the cytotaxonomic view point S. paradoxa and S. azygospora come close to each other. S. azygospora may be a mutant of S. paradoxa having lost the ability to conjugate. The wide range of variation in the nuclear and chromosomal characters in different taxa and their significance in the cytotaxonomy of the genus have been adequately discussed in the light of present and earlier studies.