CACTACEAE FAMILY

• All but one cactus species is endemic to (occurs naturally only in) the New World
• All cactuses are succulent (have water-storing tissue), but not all succulents are cactuses (e.g., Sotol). This sometimes makes it difficult to distinguish cactuses from other plants that convergently evolved (developed similar characteristics due to experiencing similar environmental constraints) with cactuses (e.g., Ocotillo).
• To be a cactus, the plant must have the following set of characteristics:
  • areoles: structures from which spines, branches, and flowers come (see picture).
  • flowers with many sepals and petals that intergrade with each other.
  • flowers with many stamens.
  • flowers with multi-lobed stigma.
• Most cactuses use CAM (Crassulacean Acid Metabolism) photosynthesis, taking in carbon dioxide at night instead of the day to save water (evaporation rates are lower at night generally), storing the carbon dioxide as an acid, and then releasing the carbon dioxide during the day for photosynthesis.
• Columnar cactuses, with leguminous trees, characterize the Sonoran Desert
• Besides columnar cactuses, other major groups include barrels, hedgehogs, pincushions, chollas, and prickly pears (see Major Types of Cactuses).