Chrysanthemum
The fall icon. Mounds of color when everything else is fading.
Toxic to cats and dogs. Chewing the leaves or flowers causes vomiting, drooling, and diarrhoea, and the foliage can irritate skin on contact. Rarely serious, but potted mums sit at exactly nose height every fall, so place them where a bored pet cannot graze.
The foliage and sap can cause a rash in sensitive skin (florists know this one well). Wear gloves for heavy pinching or division, and expect stomach upset if any part is eaten.
For gardeners who like to stay ahead.