ABSTRACT: The Donna O'Neill Land Conservancy is a 486 hectare (1,172 acre) reserve located within Cristianitos Creek watershed on Rancho Mission Viejo, southern Orange County. The Conservancy was set aside to offset impacts to the Talega Homes development site during the 1980s and is privately managed. The vegetation is primarily composed of coastal sage scrub, chaparral, southern oak woodland, sycamore riparian woodland, native needlegrass perennial grassland, and annual grassland, with scattered sandstone cliffs and outcrops. The authors conducted rare plant and floristic surveys of the Donna O'Neill Land Conservancy in 2003 and 2004. Two-hundred and forty-four taxa, representing 59 families, were collected during the survey. One hundred and eighty taxa were native and sixty-seven taxa were non-native. Twelve addditional taxa were observed but not documented. The largest plant families were Asteraceae (51 taxa), Poaceae (35 taxa), Fabaceae (17 taxa), and Scrophulariaceae (eight taxa). Twelve documented species within the Conservancy are listed in the California Native Plant Society's Inventory of Rare and Endangered Species or considered of Local Concern.