I'm a really sucker for punishment when it comes to the structure and form of plants. Take leaves for example - I absolutely love them! In fact, one of my favourite times in my garden is at the beginning of the year when there are no flowers at all but when there as lots and lots of lovely leaves in all different shapes and sizes. It's nice to see the different shapes and sizes of leaves on different plants, but even nicer to see the variety of form that you can find within a single species. Take the tomatoes in my greenhouse as a good example. All members of the same family, but structurally totally different and therefore making a totally unique contribution to the overall structure of the planting in any given space.
From top: Scatalone, Imur, Russian Red, San Marzano, Gardener's Delight, Currant