This article sheds light on Maria Bandeira, the first female botanist to work at the Botanic Garden of Rio de Janeiro. She was active in the 1920s, but is absent from the historiography and little cited in the scientific literature. The significant number of plant, fungus, and lichen specimens she collected, her capacity to reach far-flung places, her extensive correspondence with foreign experts, and her studies at Sorbonne are all sources for the analysis of the way botany was practiced and the social networks at play in science at the time. The end of her scientific career, when she adopted a cloistered life with the Barefoot Carmelite nuns, can be interpreted variously, and partially explains why her contributions to Brazilian botany have been forgotten.