A new genus and species, Calderonella sylvatica (Gramineae), is described from the rain forests of Panama. Features of its spikelet morphology and leaf anatomy reveal that the affinities of Calderonella are with the centostecoid group of grasses, of which Zeugites appears to be the most closely related genus. A brief characterization of the centostecoid group is presented, as well as a key to the genera included in it, with comments on each. In the rain forests of tropical America occur some of the most ornamental members of the grass family. The new genus is no exception. Delicate plants which inhabit the densely shaded forests of Panama (Fig. 1) in the Province of Colon, the lanceolate blades and white spikelets borne on long filiform culms create the illusion of a liliaceous plant (Figs. 2-3). Plants of Calderonella are common in the forests of Santa Rita and were first discovered by Correa and Dressler in January 1968, when access to the previously undisturbed forests was made possible by a new lumber road. Large gatherings have since been made in the same location, with field observations carried out by Cleofe E. Calderon, after whom the genus is named. The specific name alludes to the forest habitat of the new grass. Plants of the new genus also occur in the forests of Cerro Jefe, Provincia de