Abstract
In this paper, we describe two endemic tree species of Pisonia (Caryophyllales: Nyctaginaceae) from Puerto Rico that were erroneously catalogued under the single name Pisonia subcordata var. typica f. gigantophylla, misidentified as P. albida or P. subcordata, and informally named as "P. borinquena" and "P. woodburyana". The species here named as P. horneae is a rare to locally occasional tree from low elevations in the Northern Karst and the Sierra de Cayey. The other species, here named as P. roqueae, is a rare to locally common tree from mid to high elevations in the Central Mountain Range and the Luquillo Mountains. We provide an account of the taxonomical and nomenclatural history of both species, images, conservation notes, a distribution map, and a key to distinguish the species of Pisonia present in Puerto Rico.