In full honesty, it is within my own beliefs that morals (good or evil) and how one defines white or black magic is up to the individual and the society they exist within. So there are no "concrete" herbs intuned with white or black magic. The use and consideration of the herb and what you are using is for (like a good or bad purpose) is up to the person using it to decide rather they are doing something good or bad. Heck, you can even have herbs used for both white and black magic if you so choose.
Three herbs that people might consider for black magic use can include:
Licorice Root which is said to have a great influence and control over someone and their mind.
Queen Elizabeth Root which may bring men to you and force them to love you.
Hyacinth is an herb I have heard to be given a bad name by a very select group of people due to some resources suggesting that it "attacks love".
Here are two sources that I uptained those three herbs from (please note that there are far more herbs than listed):
Herbs are more commonly for individual magickal representation. There are very few herbs that are vague enough for all negative, "black" magick, most have individual magickal proporties such as rose petals being used in love spells, or sage for protection and purification.