THE REAL DIRT ON: Horace Mann Jr.

By Carol Buckley.

Perched on a slope high above the Pacific Ocean on Kauai, 20-year-old Horace Mann Jr. collected a fern (to be named Diellia mannii), which was the only plant of this species ever to be found. His travels in Hawaii with Yale professor William T. Brigham (1864–1865) and his discovery of more than 100 plant species new to science would inform Mann’s most influential work, Enumeration of Hawaiian Plants. At such a young age, he had a bright future in the burgeoning realm of American botany.

Horace was a hybrid of many influences. His father, Horace Mann, founded Antioch College in Yellow Springs, Ohio, and is known as the Father of Public Education; his mother, Mary Tyler Peabody Mann (profiled here, June 2017), translated a groundbreaking German book on school gardens, wrote a botanical book for children, and was a leading abolitionist. His aunt, Elizabeth Peabody, opened the first English-speaking American kindergarten and was a publisher. As a teenager, Horace spent several weeks with family friend Julia Ward Howe and her husband. After his father’s death in 1859, Horace, his mother, and brothers moved from Ohio to his mother’s hometown, Concord, Massachusetts. There, they rented The Wayside, home of Mary’s sister and brother-in-law, Sophia and novelist Nathaniel Hawthorne.

Ensconced in this close-knit community, Horace was mentored in nature studies by Henry David Thoreau, whom he accompanied on an expedition to Minnesota in 1861. That fall, Horace began his studies at Harvard College, where he studied with renowned biologist Louis Agassiz and Asa Gray, known as the Father of American Botany.

Gray had his eye on Horace, who became his assistant in 1866. When Gray traveled to Europe in September 1868, he left Harvard’s botanical garden and Botany Department in recent graduate Horace’s hands, hoping that Mann would take over permanently when Gray retired. Sadly, Horace died of tuberculosis in November of that year—at age 24—on the same day that he was elected to the American Academy of Arts and Sciences.

Horace left behind a collection of over 7500 species and an approximately 12500 sheet herbarium. In addition to Enumeration of Hawaiian Plants, which was his graduation thesis, he had begun the major work Flora of the Hawaiian Islands and Analysis of the Hawaiian Flora; William Brigham completed and published it after Mann’s death. The University of Michigan has a repository of many of Mann’s papers and it includes photographs he took in California’s Mojave Desert before crossing the Pacific to Hawaii.

And what ever became of the Diellia mannii, or Mann’s island spleenwort? For nearly 100 years, it was considered extinct until resource conservation technician Laura Arnold found a single specimen while weeding forest at Halemauu on northwest Kauai in 2002. Because this was the only sighting since 1906, the current listing is “critically imperiled.”