Most recent studies exploring patterns in floral development have focused on the genetic control of floral morphology. However, it has been suggested that spatial constraints within the floral meristem also play an important role in controlling number and arrangement of floral organs. These spatial constraints have been hypothesized to play a particularly important role in the evolutionary patterns of "basal" angiosperm flowers. The most commonly used model of spatial constraint postulates the existence of a primordial inhibitor that diffuses into the apical meristem from each initiated primordium. This inhibitory "morphogen" blocks the initiation of new primordia until the concentration of the inhibitor has diminished below some threshold value. Such an inhibitory model has been used to explain transitions between various floral organ arrangements. In particular, it has been cited when examining the shift between spiral and whorled organ arrangement in a single flower. Here, a three-dimensional computer model is used to test these hypotheses of floral organ pattern formation by varying parameters such as apical growth, primordial size and inhibitor release. This computer model uses the diffusion of the inhibitor to predict the number and arrangement of floral organs given a set of initial apical conditions. Here, I address two hypotheses: (i) the effect on floral morphology of varying primordial size, and (ii) the role of developmental timing, here modeled by plastochron length, in the switch between whorled and spiraled morphology. Results indicate that while some patterns are a natural outcome of the model, other proposed patterns appear to be more complex than previously understood.

Key words: computer modeling, floral development, spatial constraint