To understand the constraints on biological diversity, we analyzed how selection and development interact to control the evolution of inflorescences, the branching structures that bear flowers. We show that a single developmental model accounts for the restricted range of inflorescence types observed in nature and that this model is supported by molecular genetic studies. The model predicts associations between inflorescence architecture, climate, and life history, which we validated empirically. Paths, or evolutionary wormholes, link different architectures in a multidimensional fitness space, but the rate of evolution along these paths is constrained by genetic and environmental factors, which explains why some evolutionary transitions are rare between closely related plant taxa.

We present an empirical model of Arabidopsis (Arabidopsis thaliana), intended as a framework for quantitative understanding of plant development. The model simulates and realistically visualizes development of aerial parts of the plant from seedling to maturity. It integrates thousands of measurements, taken from several plants at frequent time intervals. These data are used to infer growth curves, allometric relations, and progression of shapes over time, which are incorporated into the final threedimensional model. Through the process of model construction, we identify the key attributes required to characterize the development of Arabidopsis plant form over time. The model provides a basis for integrating experimental data and constructing mechanistic models.Plant development is a dynamic process in which the topology and geometry change over time in a seemingly complex manner. This changing form provides the context of gene action while at the same time being under the control of gene action. To understand this process quantitatively, we first need to identify and measure the key attributes of plant form needed to specify the observed growth pattern. This can be achieved by coupling data acquisition with the construction of a model. The needs of the model guide the process of data acquisition, and the choice of parameters is eventually validated by the final appearance of the model (Bell, 1986).We present such a model for Arabidopsis (Arabidopsis thaliana), one of the key organisms used in the study of plant biology. Measurements and staging of wild-type Arabidopsis growth have been described previously to provide standards for comparisons with mutants (e.g. Smyth et al., 1990; Meicenheimer, 2000a, 2002b). Arabidopsis models have previously been constructed by De Visser et al. (2003) for the purpose of simulating a number of flowering mutants, and by Chenu et al. (2004) for the purpose of simulating light acquisition by rosette leaves. We present a more detailed model of the wild-type plant, intended to serve as a stepping stone for the integration of developmental and molecular genetic data, and for the incorporation of developmental mechanisms.Models of plant development can be implemented using a variety of methods (Prusinkiewicz, 1998). We chose the formalism of L-systems (Lindenmayer, 1968;Prusinkiewicz and Lindenmayer, 1990;Karwowski and Prusinkiewicz, 2003), which provides a programming language for describing the models and a convenient method for visualizing the results as growing three-dimensional structures. According to this formalism, a plant is viewed as a developing assembly of individual units, or modules. These modules are characterized by parameters such as length, width, and age, as well as parameters characterizing shape. A methodology for constructing L-system models based on empirical estimates of such parameters has been introduced by Prusinkiewicz et al. (1994).Here we adapt this methodology to model a developing Arabidopsis (Landsberg erecta) plant from seedling to maturity. We cons...

INTRODUCTIONThe Antirrhinum species group comprises approximately 20 morphologically diverse members that are able to form fertile hybrids. It includes the cultivated snapdragon Antirrhinum majus, which has been used as a model for biochemical and developmental genetics for more than 75 yr. The research infrastructure for A. majus, together with the interfertility of the species group, allows Antirrhinum to be used to examine the genetic basis for plant diversity.

INTRODUCTIONThis protocol describes general strategies for propagating Antirrhinum (snapdragon) species: self- and cross-pollination, cuttings, and grafting. Antirrhinum majus cultivars and some wild species are self-fertile, but they require self-pollination for high seed yields. Although self-fertile, A. majus shows unilateral incompatibility and can only be crossed to other self-incompatible species as the female parent. All Antirrhinum species can be propagated clonally from cuttings. Antirrhinum also readily forms grafts within and between species.

INTRODUCTIONIn this protocol, we describe methods for cultivating Antirrhinum (snapdragon) species. These plants are easily grown, provided that they have sufficient light and are not overwatered. In good conditions, most species will flower and produce seeds within 3-4 mo. Strongly growing plants should suffer from few pests or diseases, but we also prescribe methods for dealing with microbes and insects that commonly damage Antirrhinum.

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