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A Short Discussion of Flower Structure

An understanding of the anatomy of a rose flower as well as the terminology used to describe that anatomy, are particularly

useful in rose identification. Rose flowers are, with a few idiosyncrasies, rather typical of most flowers.The stem which connects the flower to the rest of the plant is the pedicel (ped-i-sell). It is also referred to as a peduncle, (pee-dunkl or pay-dunkl) and the two words are interchangeable IF there is only one flower on the stem. If there is a cluster of flowers, the entire cluster is supported by a peduncle, while each flower of the cluster has its own pedicel. Pedicels always subtend individual flowers; peduncles subtend entire inflorescences (which in roses may be clusters or just an individual flower). The end of the pedicel, where the stem stops and the flower begins, is the receptacle. In most non-rose flowers, the other parts of the flower are attached directly to the receptacle. However, in roses, there is a bowl-shaped hypanthium (hi-panth-ee-um), which is a combination of the receptacle and the bases of the sepals, petals, and stamens, all fused together into a single unit. The hypanthium ultimately grows to become a rose hip.

Attached to the hypanthium are four groups (whorls) of parts. The outer two are non-reproductive; the inner two are reproductive. The outermost whorl is the calyx (kay-lix). It is made up of five green, leaf-like flaps, each of which is a sepal (see-pull). The sepals cover the flower bud until shortly before it opens.

The second whorl is the corolla (kor-ol-la). Don’t say it kor-rhol-la, unless you’re referring to a model of Toyota. The corolla is made up of five large, colorful flaps, the petals. These, of course, are the most showy portion of the flower. (Double flower, i.e., those with more than 5 petals, will be explained later.)

The calyx and corolla are the nonreproductive whorls; the two of them together are referred to as the perianth. Inside the perianth is the third whorl, the androecium (an-dro-e-see-um), made up of many stamens (stay-menz). This is the male portion of the flower. Each stamen consists of a long, thin stalk – the filament, and a larger, usually yellow top portion – the anther. Pollen is produced inside the anther, which cracks open to release thepollen when the flower is fully open. You may notice that botanical descriptions often statethat a rose has an “infinite” number of stamens. Obviously, botanists must not be mathematicians! In botanists’ jargon, the word “infinite” means “more than 12″. In the case of a rose flower, it is usually substantially more than 12.

At the center of the flower is the gynoecium (jie-no-e-see-um), the female portion of the flower,consisting of many pistils. Each pistil has three parts – a knob-like stigma, onto which pollen is placed during pollination, a long, thin stalk called the style, and a large, bulbous ovary at the base, which contains a single ovule. After pollination and fertilization, the ovule grows to become a seed. The illustration at the beginning of this page shows only two pistils; a rose would normally have many (an infinite number!) of pistils. The pistils are attached inside the hypanthium, to its floor and inner walls.

I promised to discuss “doubling” of flowers. As we all know, most of the roses we grow have more

than five petals. This situation is known as doubling, and it results when some or all of the stamens become modified to look like petals. Technically, there are still only five true petals; the rest are petaloids. Because the petaloids are modified stamens, extremely double flowers often have few or no functional stamens left, and so may be male-sterile and worthless as male parents in breeding. They may still be fertile as female parents.

Since doubling results in at least partial sterility, it is seldom perpetuated in nature, and we have highly double roses only because rosarians have discovered such plants and purposely cultivated them.

Reprinted from the 12/94 issue of The Cherokee Rose

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