Carnegiea gigantea

FNA (vol. 4) accepts the name Carnegiea gigantea. The name Carnegia gigantea is used by Kartesz (1999) in his Synthesis of the North America Flora, however, it appears that the genus name represents a misspelling, as Index Nominum Genericorum indicates that Carnegia as a genus is placed in another family, other than Cactaceae (Chrsostomataceae). The spelling of the genus as applied to the cactus species is Carnegiea (Carnegiea gigantea) as per Index Nominum Genericorum. All other sources consulted regarding this cactus spell the genus 'Carnegiea' after Andrew Carnegie.

The Saguaro is only found in the Sonoran Desert, which extends from Arizona south through Sonora, Mexico. It is a keystone species to the desert habitats throughout the Sonoran Desert ecosystem. It is threatened by grazing, invasive species, poaching, urban expansion and other anthropogenic threats. For many decades this species has declined, however, census information from 2010 indicate that recruitment, as measured by the numbers of small saguaro, was substantially higher than at previous times.

The entire range of the Saguaro is from northwestern Arizona, near Kingman, to Sonora, Mexico near Navajoa. There area a few isolated populations in California, west of the Colorado River (Thornton 2008). Believed to cover approximately 19,000 sq miles in Arizona, with the highest quality habitat, linked with rainfall, is only 5% of its range in Arizona (Thornton 2008).

A number of threats exists to this iconic species of the southwestern, Sonoran Desert.

Grazing has a long established history throughout the Saguaro's range, and results in trampling seedlings and their needed nurse-plants but also cause soil compaction which reduces the water permeability of the soil (Thornton 2008).

Invasive plants, especially Buffelgrass, Cenchrus ciliaris (=Pennisetum ciliare), which was introduced to repair the landscape from grazing, increases the fuel-load across the Sonoran Desert which make damaging fire more likely to occur. Saguaro and many desert plants do not have adaptations to recurrent fire (Van Devender and Dimmitt 2006). Chemical control measures, and hand-pulling of Buffelgrass by volunteers is occurring to mitigate the effects of the invasive to the Sonoran Desert ecosystem and to the Saguaro, (Thornton 2008).

Climate change is also a threat. Distribution shifts are likely to occur as temperatures increase (Thornton 2008).

Smuggling of drugs and people, and the related law enforcement activities degrade the Sonoran Desert habitat by causing disturbance to the vegetation, erosion, and damage to the soil (Thornton 2008).

Epidermal browning causes a thickening of the plant's skin, and ultimately reduces saguaro's ability to photosynthesize causing premature mortality. While the cause of epidermal browning is not completely understood, some theories link it to ozone depletion and air pollution (Thornton 2008).

Poaching is a threat, especially of saguaro that have 'crested' (formed a fan-like structure) (Thornton 2007), but to non-crested individuals as saguaro are in demand for low-water landscaping and poachers can turn a quick profit (Thornton 2008).

Finally, development is a threat as development expands into the Sonoran Desert (Thornton 2008)..