 It was also found early on that very similar species in the same genus show large variation in genome size, despite having similar phenotypes and karyotypes (i.e., number and shape of chromosomes in a genome). Within the family of buttercups, for instance, DNA content varied up to 80-fold (Rothfels et al. 1966). Also, Holm-Hansen (1969) showed that species of unicellular algae display a 2000-fold difference in DNA content despite all being of similar developmental complexity. It was findings such as these that gave a real urgency to addressing this discrepancy that was now labelled the C-value paradox (Thomas 1971). The term ‘C-value’ refers to the constant (‘C’) amount (‘value’) of haploid DNA per nucleus and is measured in picograms of DNA per nucleus. The C-value is a measure of the amount of DNA each genome contains (we can see here Winkler’s original definition of the genome at work).