Who was Mrs. John Jones, expert gardener? The Pennsylvania Horticultural Society is digging to find out.

The colored slide of an extraordinary alpine garden remains a gem of the Pennsylvania Horticultural Society archives. It depicts clouds of pink and purple flowers, greenery sprouting improbably from every crevice of a rocky bank in Paoli.

The mastermind behind the garden, described in 1927 as one of the best rock gardeners of her generation, was Mrs. Richard Haughton.

But who was Mrs. Richard Haughton?

That basic question is at the heart of a new research project launched by PHS, aimed at uncovering the identities of 150 of Pennsylvania’s historic women gardeners in the 19th and 20th centuries. The goal is to fill out the official record in the Library of Congress and also to add life and detail to some of Philly’s green pioneers.

“People in their circle knew their names, people in their garden clubs. But they were officially known as Mrs. John Jones. Even PHS did that up until 1980,” said Janet Evans, the associate director of PHS’s McLean Library, who is leading the effort. “It’s kind of detective work.”

To fill out their biographies, Penny Baker, an archivist at PHS, is scouring birth, marriage, and death certificates on Ancestry.com, combing through church records and newspaper articles, and cross-referencing census information. Some of the gardens that PHS has on file have no listed address, because “they were simpler times when everyone knew so-and-so lives on this road,” Evans said. The project runs through June, and the society has uncovered more than 75 women so far.

The 1920s and ‘30s were a golden age of gardening in Philadelphia, said Nicole Juday, a garden historian and author of the book Private Gardens of Philadelphia. Labor and fuel were cheap, and money was pouring into the city, transforming it into the Silicon Valley of its time.

“That coincided exactly with when conspicuous consumption through gardening was at its height,” Juday said, pointing out that some of today’s most beautiful public gardens, including Morris Arboretum and Longwood Gardens, were private gardens then.

At the time, women with means were largely absent from the workforce. Gardening and horticulture offered them rare opportunities to use their minds, channel their energies, and receive recognition for their talents. While the laborers were generally men, wealthy women were the directors and producers of elaborate backyard landscapes.

Gardening was almost a loophole for intellectual pursuits: some gardeners became experts in design, while others practiced botany or made money as photographers and lantern slide colorists. (Their job was to hand-color the black and white photographs that appeared between transparent glass slides at public presentations.)

“There were so many areas that women were really overlooked and their accomplishments and contributions were minimized,” Juday said. “Gardening is one of the few areas where women could shine.”

In the case of Mrs. Richard Haughton, Baker discovered through her research that the alpine specialist’s given name was Marie Voight. She married her husband, Richard, in 1913 in Lucerne, Switzerland, where she perhaps first learned about alpine plants. In 1926, she won a PHS medal for “a rare and extensive collection of rock plants.”

In 1927, Swiss horticulturalist and rock garden expert Henri Correvon detailed a trip to a “country village called Paoli” to see the Haughtons’ garden. He wrote about how they had planted dwarf primroses, daphnes, alpine rhododendrons, small junipers, phlox, and a bounty of other plants among the rocks — all “naturally distributed in a marvelous scene which I shall never forget!”

All of the details helped to fill out Marie Voight’s biography.

Baker came across another subject, a woman named Elizabeth Bootes Clark, in a digitized gardening book originally published in the 1920s. Clark never married and had no entry in the Library of Congress Name Authority file, where researchers look for information about published historical figures. Through digging, Baker discovered that Clark earned a degree in landscape architecture and horticulture and took commissions to design other women’s gardens in the Philly area. PHS owned slides of some of the gardens she designed.

Some of the project’s findings have particularly delighted researchers. Baker decided to research a gardener listed only as Mrs. William Townsend Elliott because she was one of the first women elected to PHS’s executive council in 1919. By triangulating archival records, she discovered that the Main Line matron was known as Anna O’Keefe, who in her earlier life had performed as a comic opera singer and toured Europe with her theater troupe.

Together, the newly uncovered details help create a clearer record of who made Philadelphia beautiful.

“They were women we wanted to lift up,” Evans said.