Hundreds of species of succulent plants are native to the American Southwest. Succulents are any plant with fleshy tissue that’s adapted to store water to use during droughts. All cactus species are succulents, but not all succulents are cacti.
The leaves of cacti have evolved to thin, sharp spines, which sprout from little knobs called areoles. The sharp spines protect the juicy plant tissues from thirsty animals and provide shade, but can no longer photosynthesize. Instead, photosynthesis happens in their thick, green, water-storing stems.
Agaves and yuccas are succulents, but not cacti because they lack areoles sprouting spines, though their leaves can be edged in sharp points and tipped with a strong spine that can painfully jab hikers who stumble into them. Their tubular flowers differ from the many-petaled cactus flowers cupping masses of stamens. Agaves and yuccas store water in thickened, leathery leaves, and other tissues. The leaves or stems of many succulents are also adapted to reduce water loss because less surface area is exposed to the air.
Succulents need to support heavy, water-filled tissues, so some have developed woody skeletons like the ribs of the giant saguaros. Saguaros might be the most famous succulent of all – unless it’s the large and stately agave, whose heart can be distilled into tequila.
This Earth Note was written by Elizabeth Blaker and produced by KNAU and the Sustainable Communities Program at Northern Arizona University.
