Pityopsis ruthii is a federally endangered plant, endemic to riparian areas of the Hiwassee and Ocoee rivers in southeastern Tennessee. The population size and spatial distribution of this species along the Ocoee River has been documented since 1985, yet about 90% of P. ruthii plants are recorded within a portion of the Hiwassee River. Our ongoing population census of these localities delineates 57 discrete site occurrences and constitutes the first population baseline for P. ruthii along the Hiwassee River. Evidence indicates that P. ruthii populations are either stable or increasing along the Ocoee River. Augmentation of natural flow and subsequent invasion of competing vegetation are frequently cited as a threat to the species; however, historical aerial photography suggests significant portions of P. ruthii habitat are resistant to succession. We discuss recent evidence that a number of natural and anthropogenic stressors are challenging population sustainability, including: invasive plants, insect pests, plant pathogens, genetic incompatibility, hybridization, inbreeding depression, and habitat disruption. It remains unclear how these stressors are currently affecting plant populations.
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