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The family Cactaceae comprises many species of flowering plants with succulent (water-storing) stems. The presence of a structure called the areole sets cacti apart from all other plants. Areoles give rise to flowers, new branches, and spines. There are many different types of spines—some are soft and feathery to protect the plant from intense sunlight, while others are tough and sharp for protection. Cacti may be one of the few sources of water in arid regions, so spines prevent animals from accessing their supply of water. To prevent water loss, cacti are covered with a waxy substance called a cuticle. Another way they conserve water is by opening structures called stomata at night, rather than during the day like most plants. Stomata are microscopic pores on the plant through which carbon dioxide enters for photosynthesis.
Cacti vary in size based on their species. Perhaps the smallest cacti species is Blossfeldia liliputana, a South American plant that’s less than an inch (2.5 centimeters) in diameter when fully grown. The tallest cactus, the Mexican giant cardon, reaches over 60 feet (18 meters).
Almost all genera of cacti arose in the Americas and are distributed from Canada to Chile. They are now found in many parts of the world, especially Australia, South Africa, and Mediterranean countries.
Cacti are sometimes thought of as strictly desert plants, but many species, such as the prickly pear cactus, are found in a number of habitats.
Cacti are flowering plants that produce seeds. They are able to bloom every year, but they will produce an abundance of flowers in response to heavy rains. Flowers differ in appearance and scent to attract specific pollinators, such as insects and bats. Cacti are slow growers and can live for many years. For example, saguaro cacti can live up to 175 years. They do not grow their first arms until they are between 75 and 100 years old.
Cacti populations are stable overall. Certain species, however, are declining due to removal from the wild to be used as ornamental plants in xeriscaped lawns (landscaped areas that require little or no irrigation).
The root systems of most cacti spread out close to the surface to absorb as much rainwater as possible. Some species are so good at storing water that they can live in drought conditions for several years.
Cactus & Succulent Society of New Zealand, Inc.
Colorado State University Herbarium
University of Texas
USDA Natural Resources Conservation Service
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