Growth and survival of Azolla filiculoides in Britain. I. Vegetative reproduction.
A study was conducted to establish the low temperature responses and limitations of A. filiculoides sporophytes. In the laboratory, normal vegetative growth was shown to continue at 5°C. Reddening of plants was a response to low temperature and high light conditions which could be prevented by shading. Adult plants died after short (18 h) exposure to -4°C but survived sub-zero temperatures >-4°C. Evidence was found of seasonal changes in chill tolerance, but not in freeze tolerance. In outdoor culture, plants survived encasement in ice and air temperatures down to -5°C. Additional evidence suggested that natural populations can readily survive air temperatures much lower than this. Microclimatic effects are likely to be responsible for this discrepancy between laboratory and outdoor culture results. Three phenotypes were identified: survival, colonizing and mat forms.