Plant material was collected in lakes and streams in the North Island of New Zealand (Table 1). Plant material was collected in different habitats to ensure that growth conditions were not affecting the response to temperature and light in the experiment. This strategy ensures a good analysis on phenotypic plasticity within species because it includes a range of phenotypes from different habitats. Each species was sampled from 5 different sites, and in total, plant populations were sampled from 11 sites (Table 1). At each site macrophytes were collected at the depth of maximum biomass within their depth range. All sites were clear water sites. A water sample was collected close to the macrophyte bed where
plants were collected and two sediment samples were collected among the roots of the macrophyte bed. The samples were kept chilled while returning to the laboratory and were processed within 48 h after collection.