This collaborative project assessed the population status, demographic trends, and extinction risks of Dendrophthora bermejae, a critically endangered, host-specific mistletoe endemic to a ~70 km² area in southwestern Puerto Rico. Over 70% of the population is concentrated on privately owned lands facing immediate and severe development pressures—most notably from the proposed Esencia development project—and is restricted almost exclusively to aging, large legacy trees (Guaiacum officinale). Furthermore, the absence of mistletoes on younger hosts points to severe seed-dispersal limitations, likely tied to the decline of local specialist frugivores. By exposing these intersecting ecological and anthropogenic threats, this work provides an urgent, data-driven framework for immediate in situ conservation and habitat protection ordinances.