Perspectives of Plant Systematics

Abstract

During the last years molecular data have been shown to be essential for a modern phylogenetic analysis of plant taxa. In consequence of such additional data sets many ideas of plant phylogenies will be modified. New fields of research in systematics will be advantageous, for example to recognize and analyse the morphologically interesting parallel evolutionary lines of a plant group. It should be kept in mind, however, that one of the first attempts to use molecular methods was serology, which has been sucessfully applied for a long time. An example is given. Modern molecular biology methods, however, have still to be introduced into the mind and hand of many systematists, being exclusively trained in classical taxonomical methods. A program should be raised to support a rapid introduction of molecular methods into plant systematic research. Intensive training courses for DNA analysis and sequencing, for the handling and processing of the huge amount of data should be installed, meetings organized to exchange experiences, ideas, and results, and a network of cooperation between the working groups adapted. Since genes and gene segments of considerably different evolutionary rates exist, molecular data are available for relationship studies of high as well as low taxonomic groups. Slowly evolving genes or gene segments (e.g., rbcL) enable the resolution of plant subclasses, classes or phyla, fast evolving genes of genera, species or infraspecific taxa. The recently detected genotypic variation of Arabis alpina is a convincing example of the latter.

It is well known from classical systematic work that it might be misleading to establish a phylogeny of organisms on one character only. This is also valid for molecular characters and will be discussed. Single copy gene characters are not necessarily superior to multi-copy genes. The systematic value of multicopy genes will be discussed for the legumin gene family and sequence data for gymnosperm and angiosperm taxa. The Ranunculaceae is one of those higher plant families, where the main context of the phylogenetic relationships between its genera is already elucidated; data of six molecular markers are available (Jensen et al.; 1995). On this basis, interesting conclusions can be drawn to answer the old question whether morphological characters like nectary leaves, embryo development, or fruit characters arose mono- or polyphyletically.