Tsvi Sachs

Developmental processes and the evolution of plant clonality

Department of Plant Sciences, The Hebrew University, Jerusalem 91904, Israel

Abstract. A common type of clonal plants grows limited ramets that are connected by modified stems. Three major developmental processes are required for this clonality: the differentiation of specialized plagiotropic stems which act as spacers, the localized formation of adventitious roots, and a limitation of vertical development which is coupled with repeated rejuvenation. Intermediate forms, ones in which one of these processes occurs without the others, are readily found. Studies of apical initiation and differentiation in a-clonal plants suggest mechanisms for these processes, based on modified hormonal correlations and maturation processes within apices. The consideration of developmental processes, which has been relatively neglected, can therefore be a key to understanding the possibilities and limitations of clonal evolution. For example, comparative development points to convergent or parallel evolution, in which a similar outcome has been based on different developmental mechanisms. Considering development also throws new light on clonal organization and developmental plasticity as well as raising concrete questions that are amenable to experimental work.

Keywords

branch differentiation, development and evolution, evolutionary constraints, node counting, ramets, rejuvenation

Evolutionary Ecology (2001) 15: 4-6 (in press).