The Starfish Cactus (Echinocereus rubispinus)
The Starfish Cactus (Echinocereus rubispinus) showing succulent stem with leaves reduced to spines. The image shows the spines and stem of a cultivated specimen. This species is sometimes known as the starfish cactus, because of the arrangement of the spines in each tuft.
In the cacti the role of photosynthesis has been taken over by the stem, which contains water storage tissues and has a thick cuticle to reduce water loss. The leaves are reduced to spines, and this provides a number of advantages to the plant. The reduced leaf area reduces the rate of transpiration, while the sharp spines protect against damage by herbivores that are seeking food or water. The whiteness of the spines may also protect the stem by reflecting excess light.
True cacti (family Cactaceae) are native to the Americas. Similar adaptations are found in the unrelated family Euphorbiaceae (Spurges), in Africa and Asia.
Image by John Bebbington
The Starfish Cactus (Echinocereus rubispinus)
The Starfish Cactus (Echinocereus rubispinus) showing succulent stem with leaves reduced to spines. The image shows the spines and stem of a cultivated specimen. This species is sometimes known as the starfish cactus, because of the arrangement of the spines in each tuft.
In the cacti the role of photosynthesis has been taken over by the stem, which contains water storage tissues and has a thick cuticle to reduce water loss. The leaves are reduced to spines, and this provides a number of advantages to the plant. The reduced leaf area reduces the rate of transpiration, while the sharp spines protect against damage by herbivores that are seeking food or water. The whiteness of the spines may also protect the stem by reflecting excess light.
True cacti (family Cactaceae) are native to the Americas. Similar adaptations are found in the unrelated family Euphorbiaceae (Spurges), in Africa and Asia.
Image by John Bebbington