Variability in the expression of a rhizome architecture model in a natural population of Iris versicolor (Iridaceae)

Abstract

We identified a rhizome architecture model descriptive of a population of Iris versicolor, quantified variability in the expression of this model, identified factors affecting this variability, and generated a set of rules of growth. Morphological traits were measured on 94 clonal fragments. Patterns of branch and inflorescence outgrowth were identified, and their dependence on year, quadrat, and clone history was tested. Iris versicolor conformed to Bell's hexagonal model (Bell, A. D. The hexagonal branching pattern of rhizomes of Alpinia speciosa L. [Zingiberaceae]. Annals of Botany 43: 209‐223, 1979), but this model was not a useful predictor of individual clone development in this population. Clonal fragments of Iris versicolor most often grew linearly, produced few ramets or inflorescences, and when branching occurred, single branching was most common. Deviations from a hexagonal pattern related to resource availability affecting rhizome size: meristem fates were influenced by length of growth increments, and length was influenced by location within the population. This suggests that the hexagonal model could predict individual clone shape in particular environments. Branching angles did not depend on year or location, but were influenced by patterns of meristem outgrowth. Rules of growth described here provide a means to understand the influences of architecture on mating system, demography, and adaptation in this population.