Nightshade refers to a family of plants known as Solanaceae, which includes both edible and toxic species. Common examples of edible nightshades are tomatoes, potatoes, eggplants, and bell peppers. These plants are characterized by their flowers, which typically have five petals and their fruit, which can be berries or capsules. However, some nightshade plants are poisonous, such as belladonna and deadly nightshade. These toxic varieties contain alkaloids that can be harmful or even fatal if ingested. It's important to distinguish between the safe and dangerous members of the nightshade family to avoid health risks.