Louis Forniquet Henderson was one of Oregon's most important early botanists. During his long and vigorous career, he collected plants in virtually every corner of the state as well as in Washington and Idaho. At the time, he may have understood the flora of the Northwest better than any living person. Henderson's tens of thousands of meticulously annotated specimens—now at Oregon State University, the University of Washington, the National Herbarium, the Gray Herbarium, and elsewhere—provide a detailed record of the changing plant communities of the Northwest from the 1870s to World War II.

Henderson was born in Roxbury, Massachusetts, on September 17, 1853, the grandson of U.S. Senator John Henderson of Mississippi. His mother, Catharine Leland, belonged to a prominent Massachusetts family, and his father, John Henderson Jr., practiced law in New Orleans. When young Louis's father, a supporter of Lincoln, was murdered shortly after the end of the Civil War, his mother took Louis and his older brother North.

Directly after completing his degree at Cornell University, Henderson went West. He arrived in Oregon in 1877 and secured a position as a high school teacher in Portland. Six years later, he married fellow teacher Kate Robinson; the couple had two daughters.

Henderson's life in botany passed through a number of phases. Starting in 1877 he was teacher and principal at Portland High School. Almost from the day of his arrival in Oregon, he began collecting botanical specimens, spending many spring and summer weekends botanizing near Portland and riding trains to his favorite wildflower areas in such mountain ranges as the Blues and the Siskiyous. His early explorations also took him into Washington State, where he collected near the mouth of the Columbia and at Mount Adams.

From 1889 to 1908, Henderson moved first to Olympia, Washington, as a state botanist and forester and then to Moscow as the University of Idaho's first botany professor, teaching and botanizing throughout the state until his retirement to Hood River in 1911. He founded the UI Herbarium, which grew to 85,000 specimens, all of which, plus his personal files, burned in the Administration Building fire of 1906.

On September 8, 1923, just days before his seventieth birthday, Henderson—then living in retirement at Hood River—swam across the Columbia River from Hood River to Washington. The feat received statewide newspaper coverage and may have reached the eyes of Albert Raddin Sweetser, head of the botany department at the University of Oregon. Sweetser was searching for a curator for the Oregon plant collection at the university's herbarium, and within days the two men were corresponding. Early the following year, Henderson moved to Eugene, where, David Wagner writes, his "thoughtful curatorial abilities created one of the richest and most useful collections of northwest plants."

For the next decade and a half, Henderson spent every summer in the field collecting plant specimens. During his tenure at the University of Oregon, he enriched the herbarium by nearly 20,000 sheets. During the winters, he labeled and curated the specimens and sent exchanges to herbaria throughout the United States.

Finally, in 1939, "the grand old man of botany of the Pacific Northwest" began to slow down. His legs and eyesight faltered, and he retired to Tacoma to live with one of his daughters. Henderson died in a Puyallup nursing home on June 14, 1942, at the age of 88.

At least sixteen Northwest plant species bear the Henderson name. Among the most beloved are: Angelica hendersonii, Dodecatheon hendersonii, Erythronium hendersonii, Phlox hendersonii, and Sidalcea hendersonii.