A fungus that can cause serious lung and brain disease in HIV-infected people grows on trees in southern California. A teenager in Los Angeles working on a science project over a summer break helped researchers at Duke University in Durham, North Carolina, discover that Cryptococcus gattii grows on three species of trees near her home. The teen swabbed more than 30 species of trees to collect DNA samples and sent them to Duke for genetic sequencing. (Her father, a researcher at the University of California, Los Angeles, collaborates with the Duke scientists.) As a Duke team led by Deborah Springer explains online on 21 August in PLOS Pathogens, they found DNA from C. gattii among three of the tree samples and genetically matched the fungus to strains earlier found in Los Angeles AIDS patients. Cryptococcal disease is a common killer of HIV-infected people who have compromised immune systems, but the advent of potent antiretroviral drugs has led to a steep drop in its incidence in places where people can access the treatment.