Final answer:
Foxglove, azalea, iris, periwinkle, oleander, hydrangea, and clematis are all examples of poisonous flowers that contain various toxins harmful to humans and animals.
Step-by-step explanation:
The question is about identifying which of the listed flowers are poisonous. Not all beautiful flowers are safe, as some contain toxins that can be harmful or even fatal if ingested by humans or animals. For example, foxglove (Digitalis purpurea) contains digitalin, which is toxic to the heart; azalea (Rhododendron spp.) contains andromedotoxins which can cause nausea, vomiting, and respiratory problems; iris (Iris spp.) has irisin, which can irritate the digestive system; periwinkle (Vinca spp.) contains alkaloids that can cause a drop in blood pressure, coma, and other side effects; oleander (Nerium oleander) contains oleandrin which is highly toxic and can be life-threatening; hydrangea (Hydrangea spp.) contains cyanogenic glycosides which release cyanide when chewed; and clematis (Clematis spp.) also contains irritants harmful upon ingestion. It's crucial that plant enthusiasts and pet owners recognize these dangers associated with certain floral species. An extensive list of toxic plants can be further explored through online resources for those interested in horticulture or safety.