The rose (Latin, rosa, in Greek, rhodon) also is a symbol that has a rich and ancient history. And like the cross, it can have paradoxical meanings. It is at once a symbol of purity and a symbol of passion, heavenly perfection and earthly passion; virginity and fertility; death and life. The rose is the flower of the goddess Venus but also the blood of Adonis and of Christ. It is a symbol of transmutation - that of taking food from the earth and transmuting it into the beautiful fragrant rose. The rose garden is a symbol of Paradise. It is the place of the mystic marriage. In ancient Rome, roses were grown in the funerary gardens to symbolize resurrection. The thorns have represented suffering and sacrifice as well as the sins of the Fall from Paradise.
Thomas Worrell, "A Brief Study of the Rose Cross Symbol" http://www.geocities.com/Athens/2092/paper3.htm
In Christian art, the white rose is a symbol of purity, the gold or yellow rose a symbol of impossible perfection and papal benediction, and the red rose a symbol for martyrdom. The rose is a frequent symbol for the Virgin Mary, who is called a "rose without thorns" since she was free of original sin. This may refer to St. Ambrose's legend that the rose grew, without thorns, in the Garden of Eden. After the Fall, it became an earthly plant, and the thorns appeared as a reminder of man's sins and fall from grace. The scent and beauty remained as a poignant reminder of the lost perfection of Paradise.
Gertrude Grace Sill, A Handbook of Symbols in Christian Art