Botanical Sciences 92 (1): 89-101, 2014 TAXONOMY AND FLORISTICS FLORISTIC DIVERSITY AND DYNAMICS OF ISLA RASA, GULF OF CALIFORNIA – A GLOBALLY IMPORTANT SEABIRD ISLAND ENRIQUETA VELARDE1, BENJAMIN T. WILDER2,6, RICHARD S. FELGER3,4 AND EXEQUIEL EZCURRA2,5 1Instituto de Ciencias Marinas y Pesquerías, Universidad Veracruzana, Boca del Río, Veracruz, Mexico 2Department of Botany and Plant Sciences, University of California, Riverside, California, USA 3University of Arizona Herbarium, Tucson, Arizona, USA 4Sky Island Alliance, Tucson, Arizona, USA 5University of California, Institute for Mexico and the United States (UC MEXUS), Riverside, California, USA 6Corresponding author:
[email protected] Abstract: Isla Rasa, a small (0.68 km2) but globally important seabird island in the Gulf of California, has a fl ora of only 14 vas- cular plant species found in three vegetation zones. Signifi cant physical alteration of the island’s surface and the introduction of non-native rodents, eradicated in 1995, add restoration ecology to the remarkable biology of the island. Over a century of botanical collections and observations record a consistently depauperate fl ora, best understood in the context of extreme aridity, isolation, and elevated levels of nitrogen and phosphorus from bird guano. The shaping factor of guano on the dearth of fl oristic diversity illustrates close connection between marine and terrestrial ecosystems in the Gulf of California. El Niño events that trigger collap- ses in marine productivity and crashes in seabird reproduction bring above-average winter rainfall pulses and rapid plant growth. Two new island records are reported (Rhizophora mangle and Viscainoa geniculata). Matched photographs show signifi cant in- crease in the cholla cactus (Cylindropuntia fulgida) since 1971.