A phytohormonal perspective on contrasting pathways to clonality

Clonality is evolutionarily flexible, yet it arises through contrasting developmental pathways that are not necessarily mutually exclusive within species and differ in whether plants form adventitious shoots on roots or adventitious roots on horizontal stems. Here, we suggest that auxin-cytokinin balance offers a comparative interspecific perspective on these alternative pathways. This idea builds on a classical principle from tissue-culture studies, in which relative auxin-cytokinin balance influences whether root or shoot developmental programmes are expressed. We extend this logic from local organogenesis to naturally occurring clonal architectures, asking whether root-derived and stem-derived clonality are associated with contrasting hormonal settings. A comparative dataset of 20 Central European herbaceous species is consistent with this view. Root-derived clonality was associated with lower auxin content and lower auxin/cytokinin ratios, whereas stem-derived clonality showed higher values, with non-clonal species occupying intermediate positions. Importantly, these measurements were obtained from young plants before clonal organs were fully developed, indicating that the observed pattern characterises an early ontogenetic stage rather than the hormonal state of mature clonal organs. Whether these associations persist or change during clonal-organ development remains unresolved. We do not present this pattern as a general explanation for why particular clonal growth forms evolve. Instead, we propose that comparative hormone profiling may help link developmental regulation, clonal architecture and whole-plant ecological strategy, and provide a basis for examining how these relationships vary across ontogeny.