Research today aims to analyse the development of plant processes over evolutionary time. To obtain a representative view, a range of plant species covering at least the crucial nodes in phylogeny must be selected for an in depth analysis. Here we present Petunia as one of the available systems: as a representative of the Solanaceae it has the advantages of good culture conditions and the availability of a range of materials, techniques and strategies that can be used to research an interesting and diverse set of questions. Why an array of model systems? Plants have evolved to adapt to environmental cues and to conquer and establish new ecological niches. Changes in gene functions and their controlling networks over evolutionary time have enabled the development of innovative structures, such as the reproductive organs in gymnosperms and angiosperms and the many different plant-plant, plant-animal and plant-microbe interaction strategies. Such changes in genetic make-up have ultimately led to the development of the w250 000 extant plant species. Whereas systems biology approaches focus on a single species to obtain ultimately a detailed and integrated view of the function of all genes within a single organism, comparative biology has a broader view on (dis)similarities in specific developmental and functional pathways across a variety of plant species One of the challenges ahead for plant scientists is to analyse and to understand the level of diversification that has allowed for the astonishing degree of diversity among the members of the plant kingdom. To understand these developmental differences between species, we must compare gene function development for a range of species covering the evolutionary diversity of all species. It is clear that the scope of plant research needs to be broadened; we could begin with identifying a well-spread set of taxa that would enable us to further unravel the crucial nodes of evolutionary events that have shaped the diversity we see today in plant morphology and in the modes of reproduction and survival. The most advanced model plant species is Arabidopsis but, in spite of its success, it cannot represent all extant species [1], if only for the reason that it is not representative for 'all' plant processes and interaction strategies. Moreover, analysis above the ecotype level is hampered by the difficulty in obtaining fertile progenies from crosses between Arabidopsis thaliana and related species In June 1980, the interim steering committee of the Plant Molecular Biology Association published its first PMB newsletter. In the foreword, Petunia and Lycopersicon were mentioned as outstanding model systems (but with the remark that 'The main objection to Petunia is that it will never be an important food source.'). Among other reasons, 'the availability of true haploids, its easy tissue culture and the quality of leaf tissue for biochemical studies and macromolecule purification' were mentioned, aspects that remain important to this day. The second issue, which featured Petunia and Lycopersicon as model systems on its cover, was filled almost entirely with information on Petunia and Lycopersicon model systems. Nevertheless, in the first issue, Arabidopsis was also recommended, among others, as a good alternative model system, which was a fairly accurate prediction. Here we propose Petunia as one of the available comparative eudicot systems. We will detail its historical setting, the major technological possibilities of using Petunia as a model system and the main areas of current research. We will of course have to balance the use of Petunia with models for other groups, for example, rice for the grasses, poplar and Eucalyptus for trees and Medicago and Lotus for the legumes
