Ynes Mexia, botanist
May 24, 1870-July 12, 1938
How We are Smart by W. Nikola-Lisa, illustrated by Sean Qualls (Lee & Low Books, 2006)
Mexia discovered a new passion when she was 51. Botany. And thanks to her, more than 500 species of plants were discovered.
A very brief biographical sketch of Mexia is available on the Online Archive of California.