The Science of Botanical Art

By Dick Rauh  

Originally appeared in The Botanical Artist, Number 23


There has been discussion for some time among the board members about having a regular science column in the newsletter. Like technique and technology, botany is a subject in which all our members are interested. Dick Rauh has agreed to write a science column for us. A botanical artist and instructor in plant morphology at the New  York Botanical Garden, Dick has also recently earned his Ph.D. in botany.  

I have been kindly asked to provide a regular science column for The Botanical Artist, and before I expect anyone to take my word for anything I suspect that those of you who don.t know me (and many who do) might wish to check on my qualifications. In a similar case, I would be the first to make such a demand - besides, if there’s anything I enjoy better than painting, it’s talking about myself. 

I have been teaching the required science course in the Botanical Illustration program at the New York Botanical Garden for nearly 8 years now. I went through the program myself, getting one of the very first certificates in 1986, all this just previous to my retirement from over 35 years as an art director in a motion picture special effects company in New York City. I do paint and draw, but because I decided I was an ignoramus about things scientifically botanical, I started taking science courses to back up my new found skills, and ended up with a Masters in Plant Science in 1997, and a Doctorate in 2001. I could go on and on, but if all this doesn’t impress you at this point, all I can say is take my forthcoming pontifications with a grain of salt. 

I told Carol Hamilton I thought I should start off with very basic stuff. Hopefully for many of you, this will be old hat. It never hurts, however, to review, and often small points get lost in the translation, so bear with me, as we journey along this road. I hope to get more and more specific as time rolls on, and plan future columns on such themes as a suggested basic science library for the botanical artist, how pollination determines the form taken by many flowers, emphasis on such aspects of flowering plants as fruits and vegetative morphology, or the difference between dicots and monocots, as well as to respond to your own questions. 

Enough preamble, lets talk about the flower. I am assuming we are all aware that there exist many plant divisions that are considered .non-flowering., and included in these are mosses, ferns and conifers. The flowering plant is a latecomer in the path of evolution, but the special characteristics which it developed has made it a spectacularly successful entry, exploding in terms of speciation to the tune of 10 to 20 times more than the largest of the non-flowering divisions. It has been successful, in a wider variety of habitats, a wider ability to cope with vagaries of climate and temperature than any other form. What has mostly made this possible has been its ability to conceal, and thus protect its seeds in both the necessary functions of pollination and seed dispersal. 

Before I begin in earnest, let me first allow this qualification. I will lie a lot. Because we are dealing with natural forms, with life, as you will, there is no hard and fast mathematical formula which holds rigidly true all the time. I implore you to be especially wary if you find me using the terms ‘only’, ‘never’ or ‘always’, unless this is based on a manmade definition. Statistically the form of natural organisms falls on a Bell curve and for the most part I will be talking about facts (or quoting experts) that are looking at the center of that curve. If I have already lost you, an example. Very often we will place a species in a larger group based on, let’s say, the number of its petals. You may come along and find a particular plant in that species with a number more or less than the one all the books say is typical. This happens all the time, and there is nothing far-out about the non-conforming plant. It does, however, behoove us as botanical illustrators to fudge on the particular plant we are painting, to make it fit into the ‘normal’ pattern. 

It’s hard to believe, but now I am starting in earnest. For simplicity’s sake, we can say a flowering plant is made up of two parts - the above ground section of stem, leaves and flowers called a shoot, and the below ground section which has different functions and morphology which we call roots. Growth for flowering plants is bipolar, with the roots growing downward into the earth, and the shoot growing upwards towards light, continuously, for the active growing period of the plant. 

The place on the stem where a leaf is attached is called a ‘node’ and the distance between leaves on a stem is thus called the ’internode’. The angle made between the leaf and the stem is called the ‘axil’. Take a look, and you will always(!) find in the axil of a leaf, a bud, and this bud is called an axillary or lateral bud (as opposed to the bud at the top (apex) of the plant which is called the ‘terminal’ bud). Now here comes the first fiat that’s liable to leave me (and a goodly number of other experts) with egg on my face. But it’s a useful and meaningful platform nonetheless. An axillary bud will never produce another leaf, but only a branch or that very special branch we call a flower! Therefore a flower is always subtended by a leaf (or that special leaf associated with a flower we call a bract)! 

Concentrating on the main shoot for the moment, note that for most plants growth is concentrated in the very tip of the shoot, an area called the apex. When a plant behaves in this manner we call it ‘indeterminate’. This means that for the growing period of this plant it will continue to grow upwards, producing new shoots, stem and flowers from a small group of rapidly expanding cells called the shoot apical meristem. While for the most part whole plants are thus indeterminate, individual organs that make up the plant are not. Leaves, for example are determinate, growing to a certain size, with few exceptions, and stopping. Flowers, too, are determinate organs, organs designed specifically for reproduction, that originate from an apical or lateral bud. If as we suspect, most of the organs that make up a flower were adapted from leaves, then one of the things that happened over the course of evolution was that the space between these leaves (the internode) disappeared, bringing the four organs in close contact. 

Finally, I can make an unqualified statement. A flower is made up of four organs, which we call ‘series’ in America, and I understand ‘whorls’, in Britain. Although flowers can, and do, have less than four series, sometimes only having one, they NEVER can have more. This is because we are talking about an accepted definition here, not the old Bell curve. Let me digress a moment to talk about the word ‘series’. As far as I’m concerned it is an arbitrary choice, one of those awkward terms that is chosen because other more acceptable terms are being used with other specific meanings. Take ‘whorl’ for example. When there are more than two leaves arising from a single node we call this a ‘whorl’, so it is a logical extension to call the units making up a flower ‘whorls’, since I have just said they probably derived from leaf nodes that have gotten bunched together. The problem in unqualified use of the term ‘whorl’ is the fact that very often a single series is made up of a number of whorls. The term ‘parts’ seems a neat choice here, but botanically the word ‘parts’ is commonly accepted to refer to the units that make up a series, for example, the petals in a corolla, or the sepals in a calyx. Oops, I think I just got ahead of myself. 

Starting from the outside, the first organ in a flower is the calyx (series), made up of the sepals (parts). Generally, but far from always, this is green and photosynthetic, and its function is to enclose and protect the flower bud, and later the seed container. Next comes the corolla (series) made up of the petals (parts), and here the function is principally one of attraction. The pollen producing series is next, the androecium with its stamens (parts). The temptation here is to call this the ‘male’ organ, but the closest I can come here is to identifying the pollen it produces as the true male gametophyte, but discussion of why I am so hesitant will happen at a later time - if anyone is interested. Last and in the center, is the gynoecium (series) made up of the pistil or carpel (parts) that hold the undeveloped seeds - the ovules enclosed in an ovary. While the sepals and petals are complete in themselves. The stamens are in turn made up of two parts called the anther and the filament, and the pistil or carpel is made up of three parts, the stigma, the style and the ovary. 

Here are some more fiats, but again I make them with a clear conscience. The order of series is always the same, from outside in - calyx, corolla, androecium, gynoecium. The sepals are alternate to the petals, and the stamens are alternate to the petals, which make the sepals opposite to the stamens. When this doesn’t seem to be happening the chances are: in this particular flower there is a missing series, or one of the series is happening on more than one whorl. When a flower has all four series, we say it is complete. When a flower has the two reproductive series, the androecium and the gynoecium we call it perfect, hence a complete flower is perfect by definition. Flowers exist in many cases lacking one, two or even three series, and are considered incomplete. (If a flower lacks all four series it’s sterile, like the outer blossoms on a Hydrangea) Depending whether it is the sepals or petals missing, or one of the reproductive organs, a flower can be incomplete and either perfect or imperfect. 

These words, although seeming simple, are valid botanical terms and carry the same meaning to any botanist throughout the world. Although we tend to communicate as artists, not with words but on visual terms, the knowledge we can gain through science can only help us become more accurate and meaningful in that communication.