Botanists disagree on the exact number of species in the Rosa family of rose species, but most agree there are at least 100. In addition, there are thousands of cultivars (a group or subspecies) of roses bred for very specific colors, shapes, scents and other characteristics.
Since ornamental roses have been popular for millennia, and there is no official body governing the development of different cultivars, it is impossible to determine the exact number. Rose species can cross-pollinate with each other as well, so there have been many hybrids created by crossing two species of rose. Some of the world's most famous rose gardens, such as the Royal National Rose Society garden near London or the Rosarie du Val-de-Marne in France, have over 2,000 unique cultivars of rose.