Temperature requirements for plants vary according to species. Generally, tropical and subtropical aquatic plants grow well at temperatures between 22°C and
28°C, with growth rate slowed at lower temperatures. The optimal temperature range for a particular species is indicative of the plants native region; those species native to tropical areas may have
a relatively narrow temperature range while those from temperate areas have a much broader range. Moreover, temperate plants have a much lower temperature threshold for growth than plants from warmer regions. Such temperate weeds include
Elodea canadensis, which is a major weed in cooler south-eastern Australia, but is rarely found in the warmer regions of the north
(Bowmer et al.
1995). Emergent and floating plants growing outdoors in temperate regions may suffer frost damage where frost occurs. For example, water hyacinth often suffers mortality of leaves high in the stand canopy when exposed to frosts
(Center and Spencer
1981). The optimum temperature range for water hyacinth is 25°C to 27°C, with growth ceasing when water temperature is below 10°C and above 40°C
(Gopal 1987).
Some sensitive, tropical species may be prone to rot (leaf shedding) if subjected to large diurnal changes in water temperature or when plants are transferred from warm to cold water too quickly without gradual
acclimatisation.
