The vegetation of the Upper Watershed Zone of Naujan Lake National Park, Mindoro Oriental Province (Philippines) is a rag-tag combination of coconut-banana-citrus plantations and other minor, subsistence cultivation practices nestled in a highly logged-over lowland dipterocarp rain forest. Its flora is composed of 338 vascular plant species belonging to 263 genera and 106 families, with a composite Shannon-Weiner diversity index of H' = 5.205.

Despite the apparent absence of a well-structured, mature dipterocarp forest in the Upper Watershed Zone of Naujan Lake National Park, it appears that substantial level of natural plant diversity is being maintained along with the continuing presence of coconut-bananacitrus plantations and other cultivation practices in the area. Of noteworthy is the record of eight dipterocarp species in the Upper Watershed Zone, namely: Anisoptera thurifera (Dagang), Dipterocarpus grandiflorus (Apitong), Parashorea malaanonan (Bagtikan), Shorea almon (Almon), S. contorta (White Lauan), S. guiso (Guijo), S. negrosensis (Red Lauan) and S. palosapis (Palosapis). Furthermore, a number of species whose type locality is Mindoro Island are still present elsewhere within the Upper Watershed Zone of Naujan Lake National Park, such as: Cephalostachyum mindorensis (Bagto, Gramineae), Leucosyke mindorensis (Urticaceae), Calamus mindorensis (Tumalim, Palmae), Mezoneuron mindorensis (Caesalpiniaceae) and Elatostema halconense (Urticaceae).

Finally, there is some degree of mutual productive sustainability relationship between the highly fragmented natural vegetation and agricultural production systems now present in the Upper Watershed Zone of Naujan Lake National Park as shown by the presence of a relatively high plant diversity index (H' = 5.205).

Key words: vegetation, flora, plants, biodiversity, endemism, conservation, upper watershed zone, Lake Naujan National Park, Mindoro Oriental Province, Philippines.