# Unusual morphologies raise questions about the evolution of branching in kelps (Laminariales)

## TL;DR

The paper explores how branching structures in kelps evolved, using unusual branched individuals to understand developmental processes and their ecological impact.

## Contribution

Reports on anomalous branching in kelp species, suggesting unbranched species retain developmental capacity for modularity.

## Key findings

- Unusually branched kelp individuals show replicated morphological subunits like blades and sporophylls.
- Findings suggest unbranched kelp species may have latent developmental modularity.
- Branching may influence kelp forest habitat complexity and community dynamics.

## Abstract

Branching stipe morphologies have evolved multiple times across the kelp (Laminariales) lineage, creating morphological forms that drive the complexity of kelp forest habitats. Although branching is likely a complicated developmental process, it has evolved repeatedly through kelp evolution and the processes facilitating the emergence of branched forms from unbranched ancestors remain unclear. Here I report on abnormally branched individuals (n = 9) from five kelp species found in British Columbia, Canada that had atypical bifurcations in their stipes, creating a single dichotomous branch. One of these species generally lacks branching entirely (Laminaria ephemera) while the other four exhibit some branching but typically lack this stipe bifurcation (Alaria marginata, Laminaria setchellii, Nereocystis luetkeana, Pterygophora californica). These unusually branched individuals exhibited replicated morphological subunits distal to the stipe bifurcation, including more blades, pneumatocysts, and sporophylls than is typical. This suggests that unbranched species possess an inherent developmental capacity for modularity with autonomy in the development of individual modules that may have helped to facilitate the widespread emergence of branched morphologies. Given the role of kelp forests in coastal environments, branching may influence habitat characteristics, potentially influencing community dynamics, and is thus a trait of particular evolutionary interest. These findings highlight the need for experiments that manipulate kelp development to better characterise the ontogenetic processes of these globally important taxa.

Branching stipe morphologies have evolved multiple times across the kelp lineage, influencing the complexity of kelp forest habitats. The author reports on anomalously branched individuals from five kelp species, exhibiting unusually replicated morphological subunits such as blades and floats. These anomalous morphologies may provide insights into how morphological innovations have evolved in kelps, and offer an important area for future research.