Santiago-Valentín, E. (Herbarium, University of Puerto Rico Botanical Garden, Box 364984 San Juan 00936-4984; goetzea@yahoo.com). Amos Arthur Heller's Puerto Rico plant collecting itineraries of 1900 and 1902–1903 and their utility for the historical study of endangered plants. Brittonia 57: 292–294. 2005.—This work reports the Puerto Rico plant collecting itineraries of 1900 and 1902–1903 of Amos Arthur Heller based on the original notebooks recently located at the Herbarium of the University of Washington-Seattle. The utility of historical data for understanding original distributions of rare species is demonstrated for two Puerto Rican species: Buxus vahlii Baill. and Daphnopsis helleriana Urb.