FACTBOX: Five facts about U.S. polygamists

(Reuters) - The self-proclaimed "prophet" of a polygamous clan in an isolated desert enclave at the border of Utah and Arizona goes on trial this week in St. George, Utah, accused of arranging a marriage between an unwilling 14-year-old girl and her cousin.

Warren Jeffs, the self-described "prophet" of the Fundamentalist Church of Jesus Christ of Latter Day Saints, or FLDS, spent 15 months as a fugitive and on the FBI's Most Wanted list before his arrest in August 2006.

He could face up to life in prison for each of his two felony charges of being an accomplice to rape. He has pleaded not guilty.

Polygamy, the practice of so-called "plural" marriage subscribed to by up to 37,000 in the U.S. intermountain West, is at the center of the trial.

Following are five facts on modern U.S. polygamists and the FLDS, the largest-known U.S. polygamist sect:

* The FLDS is a break-away sect from the Church of Jesus Christ of Latter-day Saints, as the Mormon faith is formally known. The Mormon faith allowed polygamy before the Civil War and then banned it in 1890 when the federal government threatened to deny statehood to Utah.

* In Utah today, polygamy is a third-degree felony punishable by up to five years in prison, but the law is rarely enforced because local authorities say prosecuting "plural" marriages is impractical. Instead, authorities in Utah and Arizona have been targeting sex crimes, welfare and tax fraud and domestic violence within polygamous communities.

* The founder of Mormonism, Joseph Smith, took at least two dozen wives, say historians. His successor, Brigham Young, had about 20.

* Today, the Mormon church rejects polygamy, despite the practice's inclusion in its early history. Similarly, most non-FLDS polygamists renounce the practice of underage brides and say their "plural" marriages are between consenting adults.

* Members of the FLDS are estimated to number about 7,500 and live in the twin towns of Hildale, Utah and Colorado City, Arizona, an isolated community wary of outsiders. FLDS members believe the highest stages of heaven can be attained only after a man takes three wives, while women are brought up to be subservient. Those who disagree with the prophet are labeled "apostates" and are exiled.