Knowlton's cactus, also known as Coryphantha robustispina, is a unique plant with many synonyms. Some of the commonly used synonyms include Coryphantha concinna, Echinocactus knowltonii, and Escobaria robustispina. This cactus belongs to the family Cactaceae, and it is native to North America, growing in hot, arid regions. Its popular name comes from the renowned American botanist, Fred H. Knowlton, who first discovered it in 1911. Knowlton's cactus has short, cylindrical stems that grow in clusters and produce bright pink flowers in the summer. This stunning cactus is a favorite among cactus collectors and is prized for its unique shape, colorful flowers, and spiny texture.