Figure 2. Growth responses from 5 clones of Stigeoclonium tenue from the Netherlands to varying concentrations of phosphorus, ammonia, and chloride. Clones 21 and 25 are sympatric as are 29 and 34. Differences in the response of these sympatric clones are taken as evidence for local polymorphism. Differences between allopatric clones reveal the existence of ecotypes as show in growth responses. Graphs have been prepared based on data presented by Francke & ten Cate (1980).