Ephemeral pools, found worldwide and once abundant along the Pacific coast of the United States, are biodiversity hotspots that support threatened and endangered species and are highly susceptible to anthropogenic agents of disturbance and pollution. Although previously abundant in the California floristic region, over 90% of vernal pools have been lost in the state since European colonization, due to habitat destruction as a result of agriculture and other forms of land development. The remaining pools exist within a highly fragmented landscape and are often located in proximity to roads, highways, and landfills. Microplastic pollution has been observed entering terrestrial ecosystems from a variety of sources and has accumulated over decades of discardment and slow degradation. Due to their seasonal pattern of inundation and recession via evapotranspiration, vernal pools may be hotspots for microplastic accumulation and fragmentation, but to date, our understanding of vernal pools and microplastic accumulation remains limited. This study examines the occurrence of microplastics within vernal pools located in the Central Valley of California and their subsequent effects on Lasthenia fremontii, an annual herb endemic to these pools. Soil and water samples were collected from five vernal pool complexes in the Central Valley of California during the dry and wet seasons in Fall 2025 and Spring 2026. Additionally, in Spring 2026, we designed and implemented a full factorial greenhouse experiment investigating the effects of four microplastic treatments (concentrations of <2 mm polyethylene fragments- 0, 0.5%, 1.0%, 2.0%), and two hydrologic treatments (well-watered and drought) on the growth and reproductive fitness of Lasthenia fremontii. Vernal pools play a unique and essential role in supporting threatened and endangered taxa. Understanding the microplastic load within these systems and investigating their effects on an endemic plant will improve our understanding of environmental health and security, while highlighting the role terrestrial ecosystems, such as vernal pools, play in the plastisphere.