The Science of Botanical Art

The Importance of Family

By Dick Rauh 

Originally appeared in The Botanical Artist, Number 26

 

Although I am not talking here about the Vanderbilts or Rockefellers, the simile of human family characteristics and resemblance is not too far off the mark. Flower families are tied together by common features, habits and responses that have developed over great expanses of time from common ancestors. As artists it behooves us to look closely, not just at the particular plant we are painting, but at some of its closest relatives, and to perhaps stress those aspects of the plant we are painting that tie it with those relatives.

There is a great variety in the diversity or unity of particular families. Some have such strong conserved features that we can take a look at a specimen and confidently place it into a family. Others are so 'all-over-theplace' that we wonder what it was that convinced the scientists to include all those plants into one family. This, like so many of the rules of plant sciences, is subject to a great deal of controversy. There are taxonomists who are considered 'lumpers,' who place a great number of genera, with perhaps a wide range of visible characters, into a single family. By contrast there are those considered 'splitters,' who will divide similar groups of plants into separate families, based on sometimes minor features. The growing science of cladistics, with claims to a more objective approach to taxonomy, may well serve to solve many of these problems, but we may eventually be left without 'family' at all, but instead 'clade.' 

Sometimes the features that tie a family together are strictly floral, with an emphasis on reproductive series, but others have significant vegetative similarities. Linnaeus, relied heavily on the former, and his Sexual System of 1753 arranged the genera of the angiosperms on the number of stamens and carpels in the flower. Today, for us, it is still a wise precaution to count the number of parts, for very often it is just this simple fact that identifies the plant on hand, and shows whether it is typical (and thus worth replicating), or anomalous, where we will be eliminated from a juried show, not for any artistic reason, but for a botanical boo-boo. 

The whole idea of grouping plants into a hierarchy of units based on more and more specific similarities, is of course a scientific attempt bring order to the vast complexity of the Plant Kingdom. However, it does help us as artists if we have some idea of the traits, visible to the naked eye, which decided the scientists to so group. 

Before we even get down to the concept of family it is useful to remember that flowering plants are divided into two classes; dicotyledons (dicots) and monocotyledons (monocots). Although there are numerous subtle and technical (but not readily apparent) differences between these two classes, there are some very strong, visual characters that we can rely on to place our plant. The habit of dicots covers the range of forms known to plants - trees, shrubs, lianas, herbs, aquatic plants, etc. Monocots, on the other hand are almost exclusively herbaceous, (i.e. if it has bark it is probably a dicot). 

Monocots tend to have parts in threes - often with the 3 sepals looking petal-like, to form a perianth of 6 tepals and for the most part 3 or 6 stamens. Dicots, on the other hand generally have parts in 5 or 4, although the range here is much wider than the monocots, and there are examples with 1, 2, 3 or 6 and many more, usually in multiples of the common number. There are many other visual clues that place a plant in a specific class. 

The leaves of monocots are mostly without a stalk, sometimes sessile but more often sheathed, forming a sleeve around the stem, and then splitting open to reveal the lamina. Often monocot leaves are strap-like, and the venation is parallel. That is to say, the secondary veins tend to run parallel with the midrib, and the minor veins run at a 90-degree angle from the ribs, but again parallel to each other. Dicots again are much more diverse in the appearance of their leaves, but the leaves are generally petiolate (having a stalk) and the secondary veins are pinnate, looking like a feather, or palmate, fanning out from the midrib from a common origin. Here the minor veins are netted, forming intricate box like patterns. 

Keeping some of these larger grouping clues in mind I will attempt to illustrate what I'm talking about using a few of the more common families. When you come upon a species that is not on this very limited list, why not get into the habit of dissecting it, using a well-regarded reference, to double check that what you are seeing is important in the botanical scheme of things, and not some anomaly. The books I mentioned in the library article are useful here, but beware. Glimn-Lacey and Zomlefer group plants by family, and as I said before there are some families with a great diversity of form. The Bailey Manual of Cultivated Plants and the Gleason and Cronquist Manual of Vascular Plants go a step further and describe the characteristics of genera, and this might be a help in narrowing down those features we might want to stress. 

Take the Rose Family for one. Here the habit ranges from trees and shrubs to perennial herbs. Thorns and prickles are often, but not always present. The flowers can be in any number of inflorescences or solitary, and then either terminal or axillary. The leaves can be simple or compound, but have the common character of having serrate margins and stipules (stipules are the leaf-like appendages present at the point where the leaf stalk [the petiole] meets the stem). The two features of the flower that are typical throughout this very diverse family are the distinct difference between a 5-parted photosynthetic (green) calyx that is basally connate (the sepals are fused at the base) and the distinct rather fragile petals, that are five in number in species plants, but that have been hybridized for generations to increase the petal number, especially in the genus Rosa. Think for a second - roses, cherries, apples, raspberries, Spiraea and Pyracantha are all members of the rose family. 

Begonias, which have their own family, are more easily defined. They are monoecious plants - with imperfect flowers on the same plant and often on the same branch. It is easy to use the words female and male to describe them, but this is technically a misnomer. In the sporophyte generation in flowering plants that is the generation we paint, there are no 'male' or 'female' parts. The pistillate (female) flowers have inferior, winged ovaries, usually of three carpels, and three branched styles, looking like yellow chenille ram's horns. They have anywhere from 2 to 5 tepals which appear regular. The staminate (male) flowers on the other hand are strongly zygomorphic, usually of four tepals, two narrow, and two large, and an androecium of many yellow stamens, with the anthers looking like little paddles. The inflorescence is determinate, with the apical flower blooming first (a male), and the flowers lower on the branch blooming later. In tuberous begonias it is the staminate flowers that are the showy ones. 

The Mustard Family is a group with small flowers usually massed into a terminal raceme, of white, yellow, sometimes orange or purple blossoms. The common characteristic of four petals arranged in a cross gave the family its original name of Cruciferae (we now call them Brassicaceae). There are 6 stamens and one superior ovary of two carpels, attested to by two lobes on the stigma. The fruit of this family is a special flattened two-parted capsule that is often very visible on the inflorescence, lower down on the stalk. The tissue that separates the two carpels and on which the seeds lie is a translucent silvery film, and the outer walls of the capsule are valves that fall off when the fruit is ripe. There are two distinct forms of this fruit, based on proportions of length to width. Some like Honesty (Lunaria) or Sweet Alyssum (Lobularia) are almost equal, forming flattened circles or ovals. Others like Garlic Mustard (Alliaria) have very long narrow fruits. A close look reveals the botanical similarities of a two-parted flat capsule, with a papery thin silvery replum enclosed in two valves. %

Another family that is strongly conserved is Lamiaceae - the Mints. Irregular bilabiate (two-lipped) flowers, often grouped in the axils of leaves, but sometimes terminal is a common feature. Here however there are vegetative characters that help isolate this group. Look for stems that are square in cross section and opposite, decussate leaves (each succeeding pair of leaves is at a 90-degree angle from the preceding pair). This combination is an almost sure identification. 

I just realized that this column is growing way out of proportion! I have no desire to take over the whole newsletter, so I will end here. If you think that the discussion of familial traits is valuable, let me know and I will devote another column entirely to this. 

 

Lamium maculatum, .Spotted Dead Nettle,. © Libby Kyer 1996  

 

Flaming Parrot Tulips, ©Barbara Oozeerally, 2001