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Phenological studies are critical for understanding the ability of terrestrial ecosystems to respond to changes in climate. Monitoring seasonal transitions at the species or community level across large areas is challenging and expensive. One approach for lowering costs is to identify phenological guilds-groups of species that exhibit similar timing of seasonal transitions-and limit monitoring to a smaller number of species within a guild. In this study, we evaluated 23 consecutive years of monthly observations of individual species at 15 long-term study sites at the Jornada Basin USDA-Long-Term Ecological Research site to identify patterns in the onset of three phenophases-leaf-out, flower, and fruit-of 16 widely occurring species in the arid southwestern United States and to investigate the existence of phenological guilds. We conducted univariate analyses of distributions in the timing of leaf, flower, and fruit production across time and space and multivariate cluster analysis of the time series to identify coherent groups of species-site instances that exhibit coherence in timing of phenophase onsets (i.e., guilds). The six species of C-3 shrubs demonstrated greater consistency in timing of all phenophases relative to C-4 grasses. Further, we found that in all species, leaf-out occurred prior to the onset of the summer monsoon rains. Cluster analysis revealed six groups of species-site observations demonstrating high within-year concordance in timing of leaf-out and first fruit across variable site conditions and rainfall years. The six groups for timing of first fruit differed from those for first leaf in that they exhibited greater multi-species membership and within-year variability in timing. We propose that use of phenological guilds can improve the efficiency of ecosystem monitoring, predictive models of ecosystem cues driving phenological events, and land management outcomes.