The LLC herbarium was founded in 1932 through the efforts of Sister Mary Clare Metz (1907–1998) at what was then known as Our Lady of the Lake College, the first accredited institution of higher learning in San Antonio, which was started in 1895 by the Sisters of the Congregation of Divine Providence. Metz spent her adult life as a nun in this order, which sent her to college to study biology at a time when the school needed life-sciences faculty. She collected more than 1,000 specimens during her doctoral work at the Catholic University of America, where her research resulted in A Flora of Bexar County, Texas, the first detailed study of the plant life of the San Antonio area. After achieving her Ph.D., Sister Mary went on to a lengthy career teaching biology courses at Our Lady of the Lake, and also curated the LLC herbarium. She was so revered by the faculty and student body, that the building that currently houses the herbarium and other science functions is named in her honor.

The herbarium currently curates ca. 10,000 specimens with a heavy emphasis on the flora of the San Antonio metropolitan region. After Metz retired, the herbarium entered a less active phase. However, starting in 2021 the herbarium has been revitalized and increasingly is being used for teaching and research.