The sparsely populated Chihuahuan Desert has for centuries been a breeding ground for rustlers, poachers, and outlaws.
Tales still linger of corrupt cowboys stampeding herds of cattle northward through Texas, using six- shooters to defend themselves if necessary. While the practice continues today in more sophisticated fashion, lawmen are increasingly turning their attention to a different kind of desert swindler.
These thieves don't dodge the cacti that poke out of the dry earth; they stop and dig them up.
Demand for wild cactus and succulent plants is growing so rapidly that scientists and environmentalists worry about the survival of some of the rarest species in the vast Chihuahuan Desert, only 3 percent of which is protected land.
"Because of the booming market for desert plants used in landscaping, and over enthusiasm by private collectors, we are running the risk of losing certain species," says Christopher Robbins, a botanist and author of "Prickly Trade," a new report by the World Wildlife Fund in Washington.
The Chihuahuan Desert - one of the most biologically diverse deserts in the world - is home to almost a quarter of the 1,500 cactus species known to science, including many found nowhere else on earth.
This causes "cactophiles" to quiver - and sometimes go to unscrupulous lengths to obtain the next addition to their collection, says Mr. Robbins.
David Thomas understands the allure. He's been a succulent enthusiast for more than a quarter of a century. In Texas, where he lives, laws permit landowners to harvest cacti from their property or give others permission to do so, and many who view the plants as nuisances are happy to be rid of them.
"You definitely have to have the right mentality for [collecting cacti]. But just the fact that not everybody does it makes it fun," he says from his Houston home. Visitors step from his back door into his bright nursery, where he has hundreds of cacti and succulents in green pots. Most he has grown himself from seed, but some of the older and rarer varieties were field collected - that is, harvested from the wild. He and his wife, Lyn, spend every free moment tending the plants, which he estimates are worth about a half a million dollars. He isn't interested in field collection, though he admits he is not above buying field-collected plants. Instead, Mr. Thomas spends most of his time propagating the species he has.
"Used to be you could just go scrape them off the desert, just have at it. It's not like that anymore," he says.
Field collection is a tricky proposition. Instead of the lassos and horses used to rustle cattle in wild West days, today's cactus rustlers use shovels and pickup trucks.
Large barrel, prickly pear, and saguaro cacti are the most sought-after varieties for desert landscaping, called xeriscaping, which has taken off in cities such as Phoenix, Tucson, and Las Vegas.
Because of Arizona's strict laws regarding cactus harvesting, landscaping suppliers - who find it easier and faster to dig up full-grown plants in the wild than propagate them in nurseries - turn to unregulated Texas.
Between 1998 and 2001, for instance, nearly 100,000 succulents worth an estimated $3 million were shipped to Arizona from Texas.
Then there are those who pluck a cactus from a state or national park and don't realize that it's against the law, says Danny Contreras, a park ranger at the Franklin Mountains State Park near El Paso. While he has caught people driving off with truckloads of barrel cacti, yucca plants, and ocotillo trees, a more common occurrence is a solitary person digging up a single cactus for medicinal purposes or to plant in their garden.
These ignorant thieves can sometimes do even more damage because, in a sensitive environment like this, even a small change can have a dramatic effect, says Mr. Contreras. As in any environment, a whole host of animals rely on desert plants for food and shelter.
Even more shocking are the tales - who knows how tall - of cactophiles renting helicopters and rappelling into remote areas to collect rare species.
To serious collectors, the most prized plants are often found in Mexico and smuggled across the border in a purse or pocket, sometimes just in seed form. In recent years, Europe and Japan have become popular destinations for such cacti, many of which are so rare that all international trade in them is banned, says Robbins, who declined to name some of the species for fear of fueling interest in them. "That's how sensitive this issue is."
Environmentalists know that some of these species have made it out of Mexico because their seeds have appeared in trade journals and catalogues even before scientists have identified them.
Robbins's position is that existing laws against cactus collection are too complex and contradictory. He recommends that they be streamlined to allow legitimate nurseries to work toward sustainable production and exporting of cacti.
Back in his Houston nursery, Thomas is flipping through one of the trade journals and spots an ad for a dealer that reads: "We do not sell field-collected plants." Others sell such plants exclusively.
"Maybe I'm a little bit hypocritical because I will buy field-collected plants," says Thomas, pointing to a row of Ariocarpus, which are considered to be among the rarest of cacti. "But there has to be some mix. Some areas should definitely be off-limits. But other areas should be open to field collection by reputable dealers. It's just a matter of finding the right mix."