Thesis (M.S., Environmental Science)--University of Idaho, June 2014 | Howellia aquatilis, a Pacific Northwestern endemic, is highly dependent upon the ephemeral hydrology of the wetlands that it inhabits. This study aimed to understand more about the ecological needs and environmental correlates of H.aquatilis. Hydrologic, substrate, vegetative, and physical variables were assessed in 26 presence and absence ponds. Models comparing presence and absence ponds concluded that soil moisture and bulk density, habitat elevation to the river, and pond hydroperiod length best predict H.aquatilis presence or absence. Models assessing where H.aquatilis grows in presence ponds concluded that water depth and the percent cover of Phalaris arundinacea best predict H.aquatilis presence or absence. Our controlled germination experiments also indicate that soil moisture plays an important role in germination success rate. Overall, we find that local floodplain and wetland hydrology affect the soil and vegetation structure in H.aquatilis habitat, and may have important impacts on the inhabitability of different wetlands for this federally threatened species.