Most flowers are round by definition, the petals, the leaves, even when jagged have no straight angles. These arrangements use curves and round elements to showcase the flowers.
These flowerbeds were created for the national garden exhibition in Brandenburg, Germany, in 2016 (Bundesgartenschau). They show examples of how graves can be planted, and nurseries from all over Germany had small, grave-sized plots showing examples of their work. Because of the spacial limitations the displays are miniatures with every plant, every petal displayed to perfection. In fact, I saw gardeners working on the arrangements with little nail scissors clipping leaves for optimum effect.
This is for The Daily Post and more photos with the topic of rounded can be found here.