A new book on the architecture of leaves, Manual of Leaf Architecture, by Ellis, Daly, Hickey, Johnson, Mitchell, Wilf and Wing, goes into great detail, assigning names and descriptions to important characters that distinguish different leaves. Size, shape, lobing, surface texture, apex and base and margins all are fully described and named and are characteristics we should be aware of as artists.
Leaves are a vital part of a plant, and in most, the major source of food, because of their function as a photosynthetic factory. Designed to capture the maximum exposure to sunlight with a minimum expense in energy they have a flat, almost two-dimensional blade or lamina. The leaf stalk, known as a petiole also contributes to that ability, allowing the individual leaves to move in response to the position of the sun. The petiole is attached to the stem at a node, and the thickening of the stalk at that point is known as a pulvinus. Leaves are either simple or compound, meaning they are either a single unit, sometimes lobed, or made up of a series of leaflets. How the lobes or the leaflets are arranged also is a consideration of their architecture. If the lobes or leaflets arise from a single point, at the base of the lamina called the insertion point, they are known as palmate. If on the other hand they reach out more or less perpendicularly from the central axis they are pinnate, like the units of a feather.
In 1790, the German poet Goethe (who in his own right was an outstanding observer of the natural world) wrote an essay entitled “The Morphology of Plants”. In this he proposed that the origin of all floral organs were leaves, and stated that “from first to last, the plant is nothing but a leaf”. Now we are finding out that his thoughts were prescient. Evolutionary biologists are discovering, first with experiments on the small cabbage family plant Arabidopsis, and now in work in the poppy family where the petal form arose independently, that the four organs that make up the flower, calyx, corolla, androecium and gynoecium, all were derived at some point from leaves. I have been teaching this in my classes for 15 years now, and it is rewarding to find that more and more molecular studies seem to affirm this theory. Here is the thinking, not only with petals, and sepals that most obviously display the possibility of leaf derivation, but also with stamens and pistils. Common genes, or ones that have proven to be strikingly similar, appear to shape the process of petal and sepal formation in the flowers that have been studied so far. It seems, for example, the genes that create petals are controlled by a toolbox of other genes that can affect the properties that distinguish different families. Apparently the strategy of creating flower variety parallels a similar strategy in the animal world, where tool-kits of different controlling genes work on appendagebuilding genes creating all the variety of legs from insects to mammals.
There is one position on a leaf that the book uses frequently, mostly to give scientists a specific spot from which to take measurements. This is what they call the insertion point, the place where the petiole meets the blade. I have never thought much about that particular place, but it might be an important reference position when we are drawing. I have tended to use the leaf stalk, and its extension, the midrib of the blade, as a helpful guide in planning the rendering of a leaf, especially one with extreme foreshortening. Attention to that insertion point, useful in ascertaining the relation of blade size to stalk, might add another strength to accurate drawing, as we ask where it appears on that guide line, visible or not from our perspective.
In all of this, the descriptive words that are so important to scientists are only secondary for us. The most important thing I can stress about this architecture, is that we pay as close attention to the appearance of the leaves we draw, as we do the flowers or fruit that accompany them, and give the leaf the respect Goethe believed it deserves.
— Dick Rauh