From the publishers website:
Color illustrations and descriptions of 36 different plants with special properties native to Hârn. Many herbs are thought to have miraculous medicinal or other properties. Characters who can properly identify, gather, preserve, and sell good-quality herbs can earn a good living, be respected in the community, and gain useful contacts among guilded apothecaries, physicians, and arcanists.
Many herbs are used in the recipes for potions. Each herb also includes a related adventure seed.