Plants can reproduce clonally or by seeds. What are the circumstances that clonal reproduction is favoured, and which type of species are most likely to be clonal?
Above: Plants reproduce asexually via rhizomes.
Sexual reproduction from seeds is common in the plant kingdom. However, many plants reproduce through vegetative propagation or clonal growth such as sprouting from rhizomes, thus they are called clonal plants. Back in 2018, we studied the Australian flora and found that the proportion of clonal species increases with latitudes across the whole continent. Thereafter, we asked why — we would like to know the underlying mechanisms for this geographic pattern. Despite having many studies on the prevalence of sexual versus clonal reproduction and its associations with abiotic conditions at smaller scales, we still have much to learn about the circumstances under which sexual versus clonal reproduction are favoured, and which type of species are most likely to be clonal or sexual at the continental scale.
Editors’ choice / Cover article: (Open access)
Zhang, H., Chen, S.-C., Bonser, S. P., Hitchcock, T., & Moles, A. T. (2023). Factors that shape large-scale gradients in clonality. Journal of Biogeography, 50, https://doi.org/10.1111/jbi.14577.
To better understand the ecological and evolutionary significance of reproductive mode, we studied 4116 seed species and their 914456 occurrence records in the Australia flora, together with a series of factors that might influence plant clonality. In this way, we could directly compare the effects of the four plant characteristics and sixteen environmental variables on determining the likelihood of a species to exhibit clonal reproduction or not.
Plants reproduce by seeds (left panel; sexual reproduction organ of the walking stick palm Linospadix monostachya; Photo: Si-Chong Chen) and by rhizomes (right panel; clonal reproduction organ of Hydrocotyle sibthorpioides; Photo: Hongxiang Zhang).
We found that plant characteristics explained more than two times the variation in the probability of species having clonal reproduction than did environmental variables. Our findings suggest that we may need to consider species’ traits as a coordinated suite that respond to environmental conditions, rather than studying them one at a time in the future. For example, one potential direction for future research is whether big plants (e.g. trees and tall plants) tend to sexual reproduction and have greater seed dispersal ability and distances to counterbalance the longer time to first reproduction, while small plants (e.g. herbs and shorter plants) tend to be clonal reproduction and have higher seed dormancy and seed persistence in the soil. A hot topic about relationships between environmental conditions and sexual vs clonal reproduction is whether stress conditions favour sexual or clonal reproduction. Sexual reproduction is found to be predominant in stress conditions such as drought and low fertility, while clonal reproduction is common in harsh conditions, e.g. low temperature and high altitudes. Our results showed that clonality tended to be favoured when environmental resource availability was high, like high water availability and high soil nutrient conditions. Therefore, we suggest clonal reproduction may be a ‘weapon’ of plants for population expansion in resource-abundant sites, rather than as a reproductive assurance under environmental stress. This would be an interesting and important direction for future research at multiple geographical regions and scales
Our study is the first continental-scale cross-species analysis to date of plant characteristics and environmental factors in shaping plant clonality. The findings advance understanding of broad patterns in reproductive strategies and help improve understanding of species’ capacity to adapt and migrate in response to future climate change.
Hongxiang Zhang, Full Professor, Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences.
Si-Chong Chen, Full Professor, Wuhan Botanic Garden, Chinese Academy of Sciences.
Twitter: @SichongChen, @AngelaMoles