The present book was planned to show that variations in natural vegetation are wider than usually anticipated. The main study object was the most widely distributed flowering plant on the planet Earth, the gramineous common reed, Phragmites australis (Cav.) Trin ex Steudel. Numerous types of interspecific (within one particular species) variations were studied in the Kokemäenjoki River delta, Western Finland (Northern Europe), an estuary that is changing and progessing towards the sea at an exceptional pace of some 30 meters a year. Three successional classes, i.e. developmental phases, were determined based on data collected in previous field investigations. The phases - Pioneer stage, Mature stage and Regressing stage - differed statistically highly significantly from each other in each of the eight biometric (concerning plant size parameters) characteristics studied. On the basis of size parameters and values of annual primary production, the strength of the three successionalphases were classified by the order: Pioneer Mature Regressing.