Although Ynés Mexía didn't receive formal training in botany, she distinguished herself as a premier collector, gathering approximately 150,000 specimens including a new genus and several new species. Mexía overcame substantial obstacles, including emotional instability, to pursue her love of plants. Her passion advanced the field of botany.
Mexía collected most of her specimens during the 1920s and 1930s and photographs of her botanical findings were regularly published in naturalist publications of the time. Her specimen collection is currently displayed at the California Academy of Science  in San Francisco.
In 1920, Mexía started taking trips with the Sierra Club, and began taking natural science classes as a special student at the University of California, Berkeley, the following year. Botany courses particularly fascinated Mexía, and she took her first collecting trip to western Mexico in 1925 at age 55. She photographed many of the specimens in their natural habitats, then dried and pressed samples of the plants for her collection.
Far from dainty, Mexía rode horses and camped out on her collecting trips even after suffering a fall that fractured a rib. Age didn't stop her from traversing torrid rainforests and glacial mountains in search of botanical specimens. Over the next 12 years, Mexía made trips to Alaska's Mount McKinley, the Brazilian Amazon, Peru, Ecuador, Chile, and Argentina, as well as other locations in Mexico.
During her last trip in 1938, in the mountains of Oaxaca, Mexico, she complained of abdominal pains, which were the result of late-stage lung cancer. She returned home where she died later that year.