The Science of Botanical Art

When Is a Flower Not a Flower? 

By Dick Rauh 

Originally appeared in The Botanical Artist,  Number 27

 

I love to give a group of students a daisy of some kind, and tell them it’s not a flower, which of course it isn’t. But??? It isn’t one flower at all, it happens to be a collection of flowers, hundreds of them, a veritable bouquet, something we call in botany an inflorescence. Actually to be technical, inflorescence is the more general term, and what is regarded as a solitary flower. Let’s say a tulip, or a hybrid tea rose is a specialized form of this broader definition. For the most part however, when we talk about a flower, it’s the showy, single, usually terminal inflorescence we are talking about and there are many, many wonderful flowers that fit that category. The economics of floral production and the exigencies of mutations have created an alternative for the plant of massing numerous small flowers to produce the same attractive effect. Often times this occurs with much less expense in energy, and tremendous advantages, for example, in extension of the receptive time period of the pistils, or the distribution of pollen.

It is no wonder that the Asteraceae, the Composites, are one of the largest and most successful of all flowering plant families. Each of the “petals” and the hundreds of units of the disc are individual flowers, and the inflorescence’s anthesis (blooming) can last for weeks as the buds slowly ripen towards the center, continually inviting repeated visits by a whole collection of insect pollinators. 

The general form of an inflorescence takes one of two roles. Although a flower has been defined, among other things as a determinate organ, and this remains consistent (I know of no instances of branches or leaves arising from the apex of a flower), inflorescences are categorized by whether the terminal bloom is the first, or the last to reach maturity. It’s as if within the confines of determinate structure, the flowering cycle is either indeterminate or determinate. In order not to confuse you any more than absolutely necessary, we give these flowering orders different names- and then proceed to name the most typical of the inflorescences that characterize the growing habits, by that name. 

When we have an inflorescence where the oldest flowers are the lowest down on the peduncle, and the newest buds are crowded at the apex, we call that habit ‘racemose’. The most typical of the inflorescences showing this is called a ‘raceme’, and each of the flowers (some call them ‘florets’ to distinguish them from solitary flowers) is subtended by it’s own stalk called a pedicel, and generally, but not always, each of these pedicels arises from the axil of a bract. A Choke Cherry or a Pokeweed blossom is a raceme. An upside-down raceme is known as a ‘catkin’ or ‘ament’. 

On the other hand, an inflorescence where the terminal flower is first to bloom and succeeding blossoms appear later as you proceed lower on the stalk is called ‘cymose’, and the inflorescence a ‘cyme’. 

When a cyme has opposite lateral axes it is called dichasial. Check out the flowers on a Begonia to see this type of growth habit. 

When a cyme has only a single axis it is monochasial, and a special one where the lateral axes form successively on one side we have a coiled or scorroid cyme, which describes the inflorescence of a Forget-Me-Not. 

The most common forms of inflorescence (how I wish there was some good synonym for this so I wouldn’t have to repeat myself every sentence) are variations of these two basic themes. For example, when you have a racemose bloom without any pedicels; the individual flowers grow directly from the peduncle (we say they are sessile) and this is called a ‘spike’. Plantain and Gladiolus are spikes, for example - and then there are countless others, like Snapdragons with minimal pedicels that somehow come in between. 

The other variation directly on the raceme is one where the pedicels get compounded and branched and we have the ‘panicle’ represented by many grasses and flowers like the Lilac. 

Flat-headed bloomers I have seen called by both terms, but I prefer to think of them as racemose because it is almost universal in these plants that the older flowers ring the circumference with the tighter buds in the center. There are two main types here. The ‘corymb’, one in which the pedicels of the flowers run spirally up along the peduncle, arising from different nodes and consisting of different lengths to compensate and form the flat top. Characteristic of this is the Joe-pye Weed. 

The other, and more common flattopped inflorescence is the ‘umbel’, and this comes in simple and compound forms. The prime difference here is that the pedicels arise as a whorl from a single node. 

In the case of the compound umbel, both the pedicels that connect the individual blooms in the so-called umbellet to the intermediate stalk called a ray, and the rays themselves, arise as whorls from single (or very close) nodes. 

In the many variations in the Wild Carrot Family of the umbel, elegant, finely cut bracts in turn subtend these. 

Perhaps because the many disc flowers crowded into the center of a ‘daisy’ act like the flat-headed inflorescences in blooming centripetally, it might be good to include here the special form known as a ‘head’ or (if you want to impress your friends) a ‘capitulum’. 

This is a form that not only consists of numerous individual flowers grouped together to make a ‘pseudanthium’ or ‘false flower’, but for the most part two distinctively different morphologies. The outer, petal-like ring of ‘ray’ or ‘ligulate’ flowers is mostly imperfect as well as incomplete, lacking stamens and sepals. Generally the single petal (although some have discernible lobes) sits above an inferior ovary and folds at the base to enclose a style and two-parted stigma. In some species the ray flowers are sterile. 

The ‘disc’ or ‘tube’ flowers that make up the center are generally perfect, although lacking sepals, unless as some botanists argue, the chaff or hairy pappus apparent on some species can be so interpreted. The disc flower is a delightful little cylinder with five triangular lobes arching out of the top, again above an inferior ovary, and, at full anthesis, a style poking up curling its branched stigma like a pair of rams horns. Within the corolla tube the five anthers form a ring around the style, ripening early as the style pokes through with its stigma arms tightly locked. As you look at the disc flowers, snugly arranged along a double spiral, you are able to see all the stages of growth, from tight bud to fully ripened flower. Within this ‘head’ formula there are some variations- the Thistles for example, made up of all disc flowers, and Dandelions and Centaureas of all rays. 

The Arum family has a distinctive inflorescence, which relies on an associated bract to carry the advertising message and this is called a ‘spathe’. 

The inflorescence itself is known as a ‘spadix’, a fleshy cylinder on which the sessile flowers are arranged in our ubiquitous spirals. Within this group we run the range of perfect, and complete flowers, to some of the most reduced examples, consisting of a single pistil, or a pair of stamens. 

In these latter cases the male (staminate) flowers tend to run at the top of the spadix with the female (pistillate) flowers below, sometimes separated by a band of sterile blooms. The inflorescences of Palms are generally a variation on this spadix-spathe theme. 

The inflorescence of the Fig Family, consists of many imperfect small flowers lacking petals carried on the inside of a fleshy receptacle in the form of a nearly closed cup and this is named a ‘syconium’ as is the resulting fruit. 

The inflorescence of the Spurges called a ‘cyathium’, generally makes use of a colorful bract or series of bracts to act as attractants, and consists of a cup-like vessel made from an involucre, topped usually with one or more colorful and shapely nectar glands. Within the cup there are fascicles of highly reduced staminate flowers at different stages of growth surrounding a single, reduced, pistillate flower of three carpels, among silky hairs that are there for protection. 

Not all groups of flowers fall neatly into a category, and very often, probably because of the lack of any consistent arrangement, they are regarded more casually as belonging to the catchall name of a ‘cluster’. Witch Hazel and the female flowers of the Oak seem to fall into this less-defined category, but I am certain that somewhere, some diligent botanist has come up with a NAME. There are some things that are too technical for anybody’s good.