REX, Ga. — Joan Tribble held tightly to her cane as she ventured into the overgrown cemetery where her people were buried. There lay the pioneers who once populated north Georgia’s rugged frontier, where striving white men planted corn and cotton, fought for the Confederacy and owned slaves.


The settlers interred here were mostly forgotten over the decades as their progeny scattered across the South, embracing unassuming lives. But one line of her family took another path, heading north on a tumultuous, winding journey that ultimately led to the White House.


The white men and women buried here are the forebears of Mrs. Tribble, a retired bookkeeper who delights in her two grandchildren and her Sunday church mornings. They are also ancestors of Michelle Obama, the first lady.


The discovery of this unexpected family tie between the nation’s most prominent black woman and a white, silver-haired grandmother from the Atlanta suburbs underscores the entangled histories and racial intermingling that continue to bind countless American families more than 140 years after the Civil War.


The link was established through more than two years of research into Mrs. Obama’s roots, which included DNA tests of white and black relatives. Like many African-Americans, Mrs. Obama was aware that she had white ancestry, but knew little more.


Now, for the first time, the white forebears who have remained hidden in the first lady’s family tree can be identified. And her blood ties are not only to the dead. She has an entire constellation of white distant cousins who live in Georgia, South Carolina, Alabama, Texas and beyond, who in turn are only now learning of their kinship to her.


Those relatives include professionals and blue-collar workers, a retired construction worker, an accountant, a dietitian and an insurance claims adjuster, among others, who never imagined they had black relatives. Most had no idea that their ancestors owned slaves.


Many of them, like Mrs. Tribble, 69, are still grappling with their wrenching connection to the White House. “You really don’t like to face this kind of thing,” said Mrs. Tribble, whose ancestors owned the first lady’s great-great-great-grandmother.


Some of Mrs. Tribble’s relatives have declined to discuss the matter beyond the closed doors of their homes, fearful that they might be vilified as racists or forced to publicly atone for their forebears.


Mrs. Tribble has decided to openly accept her history and her new extended family.


“I can’t really change anything,” said Mrs. Tribble, who would like to meet Mrs. Obama one day. “But I can be open-minded to people and accept them and hope they’ll accept me.”


Complicated Histories


The bloodlines of Mrs. Obama and Mrs. Tribble extend back to a 200-acre farm that was not far from here. One of their common ancestors was Henry Wells Shields, Mrs. Tribble’s great-great-grandfather. He was a farmer and a family man who grew cotton, Indian corn and sweet potatoes. He owned Mrs. Obama’s maternal great-great-great-grandmother, Melvinia Shields, who was about 8 years old when she arrived on his farm sometime around 1852.


The DNA tests and research indicate that one of his sons, Charles Marion Shields, is the likely father of Melvinia’s son Dolphus, who was born around 1860. Dolphus T. Shields was the first lady’s maternal great-great-grandfather. His identity and that of his mother, Melvinia, were first reported in an article in The New York Times in 2009, which also indicated that he must have had a white father.


Melvinia was a teenager, perhaps around 15, when she gave birth to her biracial son. Charles was about 20.


Such forbidden liaisons across the racial divide inevitably bring to mind the story of Thomas Jefferson and his slave Sally Hemings. Mrs. Obama’s ancestors, however, lived in a world far removed from the elegance of Jefferson’s Monticello, his 5,000-acre mountain estate with 200 slaves. They were much more typical of the ordinary people who became entangled in America’s entrenched system of servitude.


No Easy Life


In Clayton County, Ga., where the Shields family lived, only about a third of the heads of household owned human property, and masters typically labored alongside their slaves. Charles was a man of modest means — he would ultimately become a teacher — whose parents were only a generation or so removed from illiteracy.


Melvinia was not a privileged house slave like Sally. She was illiterate and no stranger to laboring in the fields. She had more biracial children after the Civil War, giving some of the white Shieldses hope that her relationship with Charles was consensual.


“To me, it’s an obvious love story that was hard for the South to accept back then,” said Aliene Shields, a descendant who lives in South Carolina.