Fujita Tomohiro, Tsuda Naoe, Koide Dai, Fukano Yuya, Inoue Tomomi
National Institute for Environmental Studies, Ibaraki, Japan.
Graduate School of Horticulture, Chiba University, Chiba, Japan.
Ann Bot. 2025 Feb 8;135(1-2):269-276. doi: 10.1093/aob/mcae105.
The impact of urbanization on plant evolution, particularly the evolution of reproductive traits, remains largely unknown. In this study, we aimed to investigate the consequences of urbanization on the reproductive traits of Portulaca oleracea in the Kantō region of Japan. Portulaca oleracea has a unique cleistogamous reproductive system, which consists of genetically determined chasmogamous (open, CH) and cleistogamous (closed, CL) plants.
We collected seeds of P. oleracea from ten populations in rural areas and ten populations in urban areas. In a common garden experiment, we recorded the type of flowers (CH or CL), reproductive phenology and seed production.
All individuals produced either CH or CL flowers, allowing us to classify them as either CH or CL plants. We observed a significant difference in the prevalence of CH and CL plants between rural and urban populations: the number of CH plants was generally low and was particularly low among urban individuals. Compared to CH plants, CL plants showed earlier phenology and produced heavier seeds, which is consistent with stress avoidance in response to heat and drought stress conditions in urban areas.
Our findings suggest that urbanization may drive an evolutionary change in the cleistogamous reproductive system of P. oleracea. CL plants with earlier phenology and larger seeds might be better adapted to urban environments, where they are subjected to harsh heat and drought stress.
城市化对植物进化的影响，尤其是对生殖性状进化的影响，在很大程度上仍不为人知。在本研究中，我们旨在探究城市化对日本关东地区马齿苋生殖性状的影响。马齿苋具有独特的闭花受精生殖系统，该系统由基因决定的开花受精（开放，CH）和闭花受精（闭合，CL）植株组成。
我们从农村地区的10个种群和城市地区的10个种群收集了马齿苋种子。在一个共同花园实验中，我们记录了花的类型（CH或CL）、生殖物候和种子产量。
所有个体要么开CH花，要么开CL花，这使我们能够将它们归类为CH植株或CL植株。我们观察到农村和城市种群中CH和CL植株的比例存在显著差异：CH植株的数量通常较少，在城市个体中尤其少。与CH植株相比，CL植株物候较早且种子较重，这与在城市地区应对高温和干旱胁迫时的避害反应一致。
我们的研究结果表明，城市化可能推动马齿苋闭花受精生殖系统的进化变化。物候较早且种子较大的CL植株可能更适应城市环境，因为它们在城市中会遭受高温和干旱胁迫。
