The ecology of Lilaeopsis schaffneriana ssp. recurva Apiaceae (Huachuca water umbel), an endangered wetland plant, is poorly understood. In spring 2001, L. schaffneriana ssp. recurva was discovered in two areas in a dense cattail-bulrush marsh at Bingham Cienega Preserve, Pima Co., Arizona, which is located in the floodplain of the middle portion of the San Pedro River, ca. 60 km north of, and 295 m lower in elevation than, all known sites of the subspecies at the time. In autumn 2001, monitoring plots were established within the population at Bingham Cienega Preserve to document phenology and the role of interspecific competition. In one-half of monitoring plots, potentially competitive vegetation was clipped at the ground surface during autumn 2001–autumn 2002. Clipped plots censused in autumn 2001 and spring 2002 had more leaves and produced flowers, whereas no flower was present in control plots. By autumn 2002, however, persistent drought may have caused a decrease in number of leaves of L. schaffneriana ssp. recurva in both control and clipped plots. By late October 2002, all aboveground evidence of plants disappeared and leaves did not reemerge, presumably due to low soil-moisture levels related to severe drought. During the study, we discovered a herbarium specimen that documented L. schaffneriana ssp. recurva ca. 55 km downstream of the study population. More recently, we discovered a new population within the Babocomari River, a major tributary to the upper San Pedro River. These newly documented occurrences verify that L. schaffneriana extends beyond the known area occupied when the plant was listed as endangered, and is not limited to the upper portion of the San Pedro Drainage.