Roses are classified by the form and color of their flowers, seed structures, leaves, and stems. As you study them, you’ll find it useful to be familiar with these parts of their anatomy, since plant descriptions often refer to them.
Although flower is the term most often used for the showy portion of a rose plant, this structure is technically known as the corolla. The corolla is made up of petals, whose number determines whether the rose is classified as single, semidouble, double, or very double. A single flower has just one row of petals—usually 5 petals but as many as 12. A rose with 13 to about 25 petals in two or three rows is said to be semidouble. A rose with more than 25 petals, in three or more rows, is called double. A very full flower having more than 45 to 50 petals in numerous rows is known as very double.
You will sometimes see the term quartered, especially in reference to old garden roses. A quartered flower is one whose petals open in such a way that when viewed from above, the rose appears to be divided into distinct quadrants.
With some roses a solitary bloom appears at the top of the flowering stem; these are usually referred to as one-to-a-stem roses. When multiple flowers appear on a stem, the grouping is known as a spray or a cluster.
Flowers open from flower buds, which are initially covered by green leaf-like sheaths known as sepals. Collectively, the sepals and the bulbous structure below them—the calyx tube —are known as the calyx. As a flower opens, the sepals turn down and may eventually be hidden by the flower. Some sepals are small and plain; others are large and frilled.
When a flower has fully opened, thin filaments called stamens become visible in the center of the flower, which is called the disc. Stamens, the male reproductive portion of the flower, release pollen from parts at their tips called anthers. The stamens of roses are usually yellow, although sometimes they are red or maroon.
The female portion of the flower, the pistil, is located at the center of the stamens. Only its topmost portion, the stigma, can be seen; hidden below it is the style, a slender tube that leads to the ovary, where seeds form if fertilization takes place. Seeds develop from ovules, egg-like objects that are borne on structures called carpels within the ovary.
Once a rose has been pollinated—either by its own pollen or by pollen from another rose—the ovary swells and a seed-bearing fruit called the hip forms after the flowers fade. Although hips are found in some form on all roses, they are largest and most striking in old garden and shrub roses. The hips of these roses are often bright red or orange, with a characteristic pear, oval, or urn shape. So distinctive are the hips of many roses that experts can often identify the variety by its hips alone.
The main branches of rosebushes are known as canes. These arise from the crown, the point where the canes are joined to the root shank. (On roses that have been budded [grafted] to more vigorous root systems, the point where the canes are grafted to the roots is called the bud union; the bud union functions as the crown.) A new cane that arises from the crown or the bud union is often called a basal break.
Stems are growths emanating from the canes and terminating in flowers. Roses produce stems of differing lengths, depending on their class. For example, most hybrid teas have longer-than-average stems, making them good for cutting. Both canes and stems are usually covered by red or green thorns (also known as prickles), although some roses are thornless. Thorns vary in size, shape, and number. They can be so distinctive that they alone can be used to identify certain roses.
Roses have compound leaves, which are made up of several leaflets. Most modern roses have five-leaflet leaves except in the area near the flower, where three-leaflet leaves usually appear instead. Old garden roses may have seven, nine, or even more leaflets. The top leaflet, called the terminal leaflet, is attached to the rest by a small stem known as a petiole; the other leaflets have stalks known as petiolules. The base of a leaf has a winglike appendage known as the stipule; the tip of the stipule is known as the auricle.
New stem growth emanates from a bud eye in the leaf axil, the point at which a leaf joins the stem. The part of the stem between the highest leaf and the flower is known as the peduncle, sometimes referred to as the neck. Peduncles are generally thornless and soft wooded, and vary in length and thickness according to variety. Often, a small leaflike structure known as a bract appears partway down the peduncle.