Not only do southern Arizona cities get water from Colorado, Utah and Wyoming; now, they’re importing cacti from Texas.

Prickly Trade, a new study from the World Wildlife Fund, reveals that cities such as Tucson and Phoenix are importing much of their drought-tolerant landscaping from west Texas. Between 1998 and 2001, almost 100,000 succulent plants were exported from Texas to Arizona — at a value of more than $3 million. Two-thirds of those were ocotillos; other popular plants include barrel and hedgehog cacti, yuccas and agaves.

Many of the plants are common in Arizona, but are cheaper to import because Texas, unlike Arizona, does not regulate collection of its native flora. Collectors typically get permission from ranchers — who see cacti as a nuisance to livestock — to remove plants from rangeland and then sell them to nurseries. Other cacti exported from Texas are often illegally smuggled into the U.S. from Mexico.

None of the species studied by the World Wildlife Fund are immediately threatened with extinction, but demand for the plants is outstripping the natural supply. “The volumes (of plants exported) over the long term are just not sustainable,” says biologist Christopher Robbins, editor of the report. Excessive harvesting could also conspire with global climate change and habitat loss to wipe out some local plant populations.

Although conservationists applaud efforts to curb water use by xeriscaping instead of planting water-sucking lawns and trees, the report warns that “those well-intended campaigns may be mitigating one environmental problem while exacerbating another.”