An exercise in which experienced phycologists were invited to nominate ('de
sign') the phytoplankton of a lake, given a description of the physical and
chemical conditions, is reported. Few intuitively reversed the process by
which they might judge the source of a given unattributed sample on the bas
is of the algal assemblage. It is argued that the power of preferential sel
ection of particular adaptations of phytoplankton can be invoked predictive
ly through resort to Functional groups ('associations').