An “herb” can be a cactus, a flower, a seaweed, a moss, a mushroom, a grass, a vine, shrub, bush or tree. “Spices” are also classified as herbs. The parts of plants used in herbalism include seeds, flowers, fruits, leaves, barks and roots.
The word “herb” implies that the plant has a specific use. Such uses may be medicinal (goldenseal); culinary (spearmint); cosmetic (almond); aesthetic (rose) or magical (sandalwood). Many herbs enjoy a rich variety of uses.
SOURCE: The Truth About Herb Magic, Scott Cunningham