Chlorococcalean algae (s.l.) from the Ecological Park of Xochimilco, Mexico

and some of their physical and chemical water properties (temperature, pH) are similar. In the contrary, the distribution of species is very heterogeneous. Fifty per cent of species were found only in one or two localities. Moreover, the Park is located in a high altitude area (2238 m.a. s.l.) and the composition of species is similar to that found in temperate zones. In our view, if some ecological imitation exists for distribution of the "temperate" species found in this Park, it could be related to environmental factors like climatic light (photoperiod) as the Park is located in the parallel 19°.