Comparison of life history characters of broad-leaved species of the genus Potamogeton L. I. General characterization of morphology and reproductive strategies

Abstract

A short historical outline of the development of the study of Potamogeton life history is given. Seven levels of research (population, genet, clone, patch, shoot complex, vertical shoot, modular unit) are defined and their appropriateness for studying Potamogeton ecology is discussed. The patch, the shoot complex and the vertical shoot are the central research units. A morphological analysis of the shoot complex is given in order to display the special properties of this important entity. Two basic shoot types are distinguished: the vegetative shoot (represented as either the horizontal or vertical shoot) and the sexual shoot. Based on the morphological description, a conceptual growth model is presented comprising the observed transitions between plant parts in the species studied. Five different reproductive strategies can be distinguised, which differ among the species studied. Data on the life span of different entities (genet, shoot complex, vertical shoot) of the species studied are compared. The life span of vertical shoots varies from short-liver (2 months) to biennial. The life span of shoot complexes varies from annual to very long lived. In most species, the genet is potentially immortal owing to extreme fragmentation. No direct correlations are found between reproductive strategies and environmental conditions expressed as stress and disturbance. Similar unfavourable conditions can be overcome by various strategies.