With some species reaching over 10m in height, the cactus defines many of the landscapes in which it lives.
Cacti have developed spines which allow less water to evaporate through transpiration by shading the plant, and defend the cactus against water-seeking animals. Most cacti have very shallow roots that can spread out widely close to the surface of the ground to collect water, an adaptation to infrequent rains.
How are cacti important?
Humans have used cacti since the time of the Aztecs, and they are used by North American Indians for religious ceremonies. Today they are used as food (jam, fruit, vegetables) and are a host for the cochineal insect, from which a red dye (carmine) is obtained.
For many animals such as the bighorn sheep and the antelope ground squirrel, cactus are an important source of food and water. The cactus wren and California thrasher often build their nests in the buckhorn cholla. The gila woodpeckers and gilded flickers chop burros in the long arms of the Saguaro Cactus.
What are the main threats to cacti?
The key threats to cacti are illegal seed and plant collection and habitat loss. Some species have been so extensively collected the population size has reduced by as much as 95% over the course of 25 years. As a result, there are as few as 50 plants surviving in certain species. Whilst all cacti species are covered by CITES, additional controls are needed, particularly in importing countries.
Habitat loss due to road construction, mining for quartz or charcoal, deforestation and the resulting erosion also threatens many cacti species. As a result, some species are restricted to an area as small as 1km2
A more recent threat is climate change
, which impacts on other species such as monarch butterflies which pollinate cacti species; and poses a threat to some cactus species through rising sea levels.