Fibonacci spirals in a brown alga [Sargassum muticum (Yendo) Fensholt] and in a land plant [Arabidopsis thaliana (L.) Heynh.]: a case of morphogenetic convergence

Alexis Peaucelle,Yves Couder

doi:10.5586/asbp.3526

Abstract

In this article, the morphology of a brown alga is revisited and compared to the phyllotaxis of land plants. The alga, <em>Sargassum muticum</em> (Yendo) Fensholt has a highly organized thallus with a stipe, the stem-like main axis, and hierarchically organized lateral branches of successive orders. Around each of these axes, the lateral organs: blades, side-branches, and receptacles grow in a spiral disposition. As in land plants, this organization is related to an apical mode of growth. Measurements performed along the mature differentiated axes as well as in their meristematic regions confirm the similarity of the large-scale organization of this brown alga with that of the land plants. In particular, the divergence angle between successive elements has similar values and it results from the existence around the meristem of parastichies having the same Fibonacci ordering. This is remarkable in view of the fact that brown algae (Phaeophyceae) and land plants (Embryophyta) are two clades that diverged approximately 1800 million years ago when they were both unicellular organisms. We argue that the observed similarity results from a morphogenetic convergence. This is in strong support of the genericity and robustness of self-organization models in which similar structures, here Fibonacci related spirals, can be obtained in various situations in which the genetic and physiological implementation of development can be of a different nature.

Highlights

Phyllotaxis concerns the arrangement of the leaves around the stems of plants
It is established by phylogenetic analysis that the most recent common ancestors to green plants and brown algae were unicellular eukaryotic organisms and that the divergence between these two clades (Fig. 1) occurred approximately 1800 million years ago (Mya) [1,2,3]
If we link the appendages in their order of appearance, the resulting curve forms a single helix. This is analogous to the land plants generative spiral

Summary

Introduction

Phyllotaxis concerns the arrangement (taxis) of the leaves (phyllon) around the stems of plants With this definition there can be, strictly speaking, no phyllotaxis in brown algae (Phaeophyceae). They do not belong to the same lineage as land plants and they do not have structures that are equivalent anatomically or physiologically to stems or leaves. Some brown algae have a morphology that resembles that of the aerial part of land plants They usually have an axisymmetric stem-like structure (a stipe) with lateral branches.

Methods

Results

Conclusion