Decades of hybridizing blurred the lines among rose cultivars. Although growers categorize roses in different ways, roses fall into four main groups: modern roses, old roses, species roses and shrub roses. This follows a chronological division more than a botanical one, and other enthusiasts sort roses according to their own standards.
In 1867, Jean Baptiste-Guillot introduced "La France," the first hybrid tea rose. Roses in this category include hybrid teas, grandifloras, polyanthas, miniatures and floribundas. Hybrid tea roses outsell all other rose varieties combined, according to the University of California Extension, and grow one flower to a stem. Grandifloras and floribundas produce flowers in clusters and may grow 8 to 10 feet tall. Growers developed polyanthas in the late 1800s, and these nearly ever-blooming, low-growing roses have small flowers. The flowers of modern roses are the classic rosebud shape and are those seen in florists' bouquets.
Classes that existed before the introduction of the hybrid tea rose are considered old roses, even though growers still develop new varieties. Damask roses, Bourbon roses, moss roses and tea roses are among the many roses in this category, but the most well-known roses are the hybrid perpetuals. Before the hybrid tea rose dethroned them, hybrid perpetuals were the popular choice for gardens. Hybrid perpetual flowers are large, often 6 inches across. The blooms of old roses are highly fragrant and the buds are shorter than hybrid tea buds. The flowers often have a pom-pom or peony form.
Species roses are the original rose and include climbers and hybrids, according to the "Sunset Western Garden Book." The nearly thornless, double-flowered Lady Banks' rose (Rosa banksiae) grows to incredible sizes, including a Lady Banks' rose in Tombstone, Arizona, that covers 9,000 square feet. Many varieties in this category have single flowers and passers-by may not recognize it as a rose. Rosa rugosa, an extremely tough rose, has cultivars with carnation-like flowers.
A catch-all category, shrub roses are hybrids that don't quite fit in any other class. Growers call them shrub roses not because of their form, since all roses are shrubs, but for their use in the landscape. David Austen roses, hybrid rugosa roses and Meidiland roses all fall into this category. They are hardy and disease-resistant, and the modern shrub roses are compact and flower freely without deadheading. The flower forms range from classic tea rose shapes to simple, single blooms.