Interactions between physical and biological constraints in the structure of the inflorescences of the araceae

Abstract

A study of the inflorescences of Monstera and Anthurium was used to establish a relationship between biological and physical constraints for the structure of plant organs. The physical constraint between flowers in the compact inflorescences of Anthurium and Monstera is expressed by Aboav-Weaire's law. The application of this law to inflorescences indicates a linear relationship between the number of sides of a flower and the number of sides of neighbouring flowers. However, the slope of this straight line is significantly higher for Anthurium and Monstera than that expected in theory. This deviation from the law is attributable to a biological cause that can be estimated using Aboav-Weaire's law. Acting alone, the biological constraint tends to produce four-sided flowers. The equilibrium between biological and physical constraints reduces the number of sides per flower from six (theoretical value) to 5.9 (in Anthurium) or 5.8 (in Monstera) with a variance of the measures less than that expected in theory. Furthermore, when flower density in an inflorescence increases (towards the middle of the inflorescence in Monstera and towards the lower section for Anthurium) the number of sides approaches six (i.e. the physical constraint dominates). When flower density decreases (towards the top of the inflorescence) the number of sides approaches 5.5 (i.e. the biological constraint dominates). The geometry of the inflorescences of Anthurium and Monstera is the result of the joint action of biological and physical constraints.