As the name implied, undead bloodroses had petals the color of fresh blood. The petals would darken until they were black if deprived of sustenance.
Undead bloodroses were beautiful but sinister flowers. The flower rooted itself in bonemeal, which was common in the passages of the Rose Garden. If cut and pinned to a lapel or other item of clothing worn by a living creature, the plant remained fresh so long as the host lived. However, the undead bloodrose slowly consumed a host's lifeforce, draining them bit by bit until they finally fell into death. Those killed by this flower rose as undead themselves. When separated from a host, the plant would turn jet black, but the blood-red coloration would return if another host was found within three or four days. If another host was not found after that time passed, then the flower would explode into a fine greenish black dust. It remained unknown if this dust had any effects on living creatures.