Abstract: The paper studied the mechanism of adaptation of Alternanthera philoxeroides (Mart.) Griseb to the change of water factor, by cultivating them in three groups of slots and manipulating their water condition to make them form three kinds of habitat types namely terrestrial, emergent, and floating types; Implementing OneWay Anova analysis and factor analysis to the following morphological parameterslength of internode, maximumcircumference of internode, branching frequency, number of adventitious roots, length of adventitious roots, leave ship index, it is revealed that the change of water factor affected all the parameters significantly. On the part of the terrestrial type, the growth of the overground parts was predominant for occupying spaces, and then of underground parts secondly; However, as for the floating type, the widenning growth of the stems and the increase of roots go up to a vital position, and the lengthening growth of them is secondary. For the emergent type , the number one growth involves double features of the former two, but the number two growth ,to a much degree, is similar to the floating type. Along the line as terrestrial typeemergent type floating type, the role of the parameter, the amount of adventitious roots, protrudes gradually. Branching frequency is always the important element to consist the first common factor, but its mean value was the smallest in floating type. Therefore, it should be a proper way to control the branching for harnessing the terrestrial and the emergent type, while to constrain the rooting for the floating type, and the relatively successive study should be based on searching for the mechanism of branching and rooting.

Key words: habitat type, Alternanthera philoxeroides (Mart.) Griseb, morphological adaptation, water