The Lehman family tree includes a governor, a chief justice of the New York State court of appeals, a secretary of the treasury, two ambassadors, members of the U.S. House of Representatives, the House of Lords, and the House of Commons, and a New York State parks commissioner. So, when descendants of one of America’s most prominent German Jewish dynasties gather later this month, it will be no ordinary reunion.

Some notables are no longer alive to attend the gathering, such as Governor Herbert Lehman, for whom Lehman College is named; Robert Lehman, who gave his renowned collection to the Metropolitan Museum of Art, and the founders of Lehman Brothers, which grew to become the country’s sixth largest investment banking house by 1950. Prominent attendees among the current generation of Lehman relatives who will be there include District Attorney Robert Morgenthau (related through his mother), who is hosting the event at the Museum of Jewish Heritage, and a former ambassador to Denmark, John Loeb Jr.

At about 150 people, it will be the largest such gathering since members of the Lehman family came together at the Metropolitan Museum about 15 years ago.

The Lehman family has much to celebrate. The stated purpose of the gathering is to celebrate the publication of “Lots of Lehmans: The Family of Mayer Lehman of Lehman Brothers, Remembered by His Descendants” (Center for Jewish History), an anecdotal history gathered from numerous Lehman family members.

After arriving in New York from Bavaria via Montgomery, Ala., the Lehmans rose to make their mark in many fields, such as finance, philanthropy, and culture. You know your family is old money when one member, Edith Altschul Lehman, the former governor’s wife, referred to the Rockefellers as “nouveau riche.”

“Lots of Lehmans” shows what it was like “to grow up in the very bosom of ‘Our Crowd,” the book’s editor, Kenneth Libo, who co-authored “World of Our Fathers” with Irving Howe, said.

The Lehmans were a quintessential American success story — even as they faced snubs from the Wasp establishment.

The granddaughter of Clara Lehman, June Bingham Birge, told The New York Sun how while she was in eighth grade her aunt and uncle invited her to ask a friend to dinner at a speakeasy followed by a musical. When she asked a friend from Greenwich, Conn., a restricted community, the youngster later replied, “Mummy and Daddy said I can’t go because if you are seen in New York with Jews, then no one will dance with you at your debut.” (The parents later relented, saying their daughter was so young that people wouldn’t remember if she was seen with Jews.)

Wasps could sometimes seem more open to Judaism than the assimilated German Jews. A Lehman descendent, William Bernhard, told the Sun about a dinner at his aunt and uncle’s house in Westchester in the early 1950s. Tennis player Palmer Dixon sat next to Mr. Bernard’s grandmother, Adele Lewisohn Lehman. When discussion turned to some family connection, “Palmer, an epitome of a wasp gentlemen, said, ‘Oh, you mean that’s your mishpocha [family].’ The response was total silence.”

The leading German Jewish elites were close knit, marrying into each other’s families. For example, Irving Lehman’s wife, Sissie, was the daughter of Nathan Straus, co-founder of Macy’s. They summered at enclaves such as Elberon, N.J. and Lake Placid, N.Y., joined the Harmonie Club, and attended New Year’s parties at Adolph Lewisohn’s, whose home at 881 Fifth Ave. naturally contained a ballroom.

The Lehmans were close geographically, too. Family matriarch Babette, who lived on the Upper East Side, insisted her children visit her daily. Jewish matriarchs, Ms. Birge said, could be brutally honest. She was reminded of this upon recently running into 94-year-old Kitty Carlisle Hart on Fifth Avenue. “Your glasses are dirty,” Ms. Hart said. “Your teeth are clean, but your glasses are dirty.”

Ms. Birge told the Sun that she thought, “My God, here’s grandma, Clara Limburg, in modern garb.”

The Lehman family made important contributions to cultural institutions. But not all art decisions in the family were so auspicious. A great-grandson of Mayer Lehman, Sir Philip Goodhart, recalled how his grandfather in the early 1900s was walking home and saw in the window paintings by an unknown Frenchman. He bought six Renoirs and his wife sent them back, thinking them indecent.

A professor at Brandeis University, Jonathan Sarna, said what was remarkable about German Jews was how rapidly they were able to rise in one generation. He said they ventured out across America to live, including the South. Ms. Birge said she was embarrassed when she learned Mayer owned slaves.

These days, after a long period, there is again a direct family connection to the Lehman Brothers. Ambassador Loeb told the Sun that his son, Nicholas Loeb — a great-great grandson of Mayer — had started working at the company’s Palm Beach, Fla., office. No word on whether he’ll be able to break away and travel north to attend this month’s gathering.