Black roses are symbols for many of the darker aspects of the universe, including death, mourning, evil, witchcraft and revenge. While there is no such thing as a natural black rose, there are roses of such a dark red that they appear black. Florists have also been known to color roses by adding dye or ink to vase water.
English people referred to Ireland as "the Black Rose" during an era when it was illegal to reference the country by name. This was likely owing to the fact that, at the time, a branch of Irish druids wore black cloaks emblazoned with the image of a rose. The term continued to be used for some time after prohibition against speaking the name Ireland was lifted.
On occasion, the black rose has been known to symbolize anarchy. In fact, Montreal's Black Rose Books publishes books targeted at those who participate in the anarchist movement.
Black roses appear in a number of anime series, including "Revolutionary Girl Utena," in which they represent the darker side of an individual's soul. Many of those with a dark sense of humor as well as those who relate to the Goth subculture enjoy giving and receiving black roses as gifts.