The Changes in Morphology and Demography of Iris pseudacorus L. at Different Heights on a Saltmarsh

Abstract

Leaf height and spacing of ramets of Iris pseudacorus L. vary down the shore of a saltmarsh. Rhizomes were studied at two sites at different levels on the shore and compared with two terrestrial sites. The age, growth, flowering and mortality of buds could be determined from the rhizome morphology. Seasonal variation in the amount of storage material resulted in a series of annual 'bulges' from which the growth history may be inferred. On the higher site on the saltmarsh, genets were very long lived and seedlings were rare whilst on the lower site there were considerable numbers of seedlings and genets were short lived. On the upper sites the growth rate of the bulges was higher and the annual bulges in the rhizomes were larger. Bulge area had a small effect on the leaf height and number of leaves on the lower site. Mortality of terminal bulges was markedly higher on the lower site than on the higher with the result that much of the rhizome growth was through lateral bulges. Larger bulges had a lower mortality rate. Laboratory experiments in which rhizomes were immersed in salt-water reproduced many results shown in the field. Key-words: Clonal growth, Iris pseudacorus, morphology, rhizomes, salinity