Professor Emeritus, San Diego State University (https://plants.sdsu.edu/simpson/).
Specialties: Plant systematics, taxonomy, floristics, American Amphitropic Disjuncts (see: https://plants.sdsu.edu/AAD/), Popcorn Flowers (subtribe Amsinckiinae, Boraginaceae; see: https://plants.sdsu.edu/amsinckiinae/). Author of textbook Plant Systematics: (https://shop.elsevier.com/books/plant-systematics/simpson/978-0-12-812628-8).