This study, involving critical plant collections from the University of Michigan expeditions and collaborating collectors, describes one new genus, fifty new species, and one new variety from Mexico, British Honduras, Guatemala, Costa Rica, Panama, and Puerto Rico. The new genus Onohualcoa in the Bignoniaceae includes a species from the Yucatan Peninsula. Alongside notes on other plants, the volume proposes two new combinations: Sideroxylon Matudat Lundell is reclassified as Dipholis, and Licaria triandra is reclassified to Acrodiclidium, consistent with the writer's view against using the generic name Licaria. The publication was funded by the Horace H. Rackham School of Graduate Studies at the University of Michigan.