The Science of Botanical Art

Alternates & Opposites

By Dick Rauh

Originally appeared in The Botanical Artist, Volune 13, Issue 2


We are familiar with the terms alternate and opposite as they apply to the arrangement of leaves along a stem. But to restate the definitions, alternate is a spiral form, where there is only one leaf to a node. Opposite means there are two leaves to a node, and the leaves are directly opposite one another. Hence the name. 

These terms are also applied to the arrangement of series and parts in a flower. Familiarity with this relationship of petals, sepals and stamens is another example of what separates the kids from the pros in this field. Looking closely and knowing what to expect can make the difference between a lovely painting and a lovely accurate painting likely to be accepted in a show where there are botanists on the jury. 

In the case of a flower, alternate means a petal (the part) lies directly in-between two sepals. This means the centerline of the petal falls right where two sepals meet. Stamens are alternate to petals. A stamen lies directly where two petals meet. In the way two negatives make a positive, the stamen, being alternate to a petal (which is alternate to a sepal) is opposite to the sepal. It lies directly above the center of the sepal. This proves true most of the time no matter what number of parts is typical of that particular flower. Often calyxes and corollas have the same number of parts. Stamens are often the same number as the parts of the perianth, or a multiple of that number. 

When you have different numbers of parts in succeeding series the rule may break down. In the lily for example, you have six stamens and three petal-derived tepals. In point of fact you have two whorls of three stamens each. The outer whorl follows the rule but the inner whorl coming in between the outer one is opposite the petals. In members of the rose family where there are numerous stamens; it is the corolla and the calyx that are visibly alternate. Take care with orchids. In some you can still identify the sepal-derived tepals as alternate to the petal-derived tepals, in spite of the unusual lower petal, the labellum. In others the two lower sepals and fused together, and they appear opposite to the labellum. 

Thus in the natural world the arrangement of petals doesn’t always fall into the neat rules we would like. Not all petals are distinct or separate from one another. Sometimes there is overlap. It is a good idea to check for this and to determine (considering your point of view) what is in front and what in back. You do have to observe carefully and check whatever references you trust, to make sure what you are looking at is not some anomaly. The petals of the mallows while alternate to the sepals, are also imbricate. This means each petal is in front of an adjoining petal and behind the next petal. In the irregular corolla of the legumes, if you are looking directly at the bloom, the top, banner petal is behind the two wing petals, which in turn cover the joined keel petals. In a pansy the lowest petal is in front of (just about) the two lateral petals that tend to meet at one place forming a triangular opening with the lowest petal. The two remaining petals are behind the side petals and the one on the right is in front of the other. As far as I can determine whether this is true in all cases is at the caprice of the particular flower but there is never any problem observing this. 

Sometimes sepals are fused into a cup or the petals may be fused into a tube. The rule still applies however. The lobes, that are the visible remainder of the individual parts, still fall into an alternate arrangement. 

Knowing where these parts originate is another clue to drawing an accurate and therefore beautiful and satisfying blossom. This usually means tracing the part back to the receptacle that falls on the center axis at the base of the flower. Think of it as a small platform that supports the bloom. Try to visualize the angle of that platform when drawing your flower. Most of the time this is hidden from view, so you have to do a little mental manipulation. The series origins on the receptacle follow the familiar pattern. The sepals are attached at the outermost whorl. The petal origins come next, followed by the stamens. In the center is the gynoecium. 

This knowledge might fortify your preliminary sketch even with the obstacle of forced perspective. For example, the line of the filament logically reaches back to its attachment point on the receptacle, even though that point is hidden from view. This assures your viewer that you know the stamens aren’t coming out of the top of the pistil, or arranged in a random, chaotic pattern. 

But take care, because not all genera have stamens that are attached to the receptacle. Very often, especially when the corolla is fused into a tube, the stamens can be attached somewhere along that tube. In these cases the line of the filament, if indeed it is visible at all, would come at an entirely different angle than if it were attached at the base. Here again a reliable source of information on the morphology of the flower, like the Zomlefer book, or the Internet, will set you straight. It’s hard to over-emphasize the importance of the logic of this confirmation to an axis. Getting it right means the drawing will look natural, not distorted or lopsided. A sound drawing is the basis for an accurate, beautiful painting. 

All of this just follows my constant admonitions: observe carefully and know what you should expect to see.