Using a 33-year-long dataset spanning a 1267-meter semi-arid elevational gradient in the southwestern United States, we test whether flowering phenology diverged among subpopulations within species and among five communities comprising 590 species. Applying circular statistics to test for changes in year-round flowering, we show flowering has become earlier for all communities except at the highest elevations. However, flowering times shifted at different rates across elevations likely due to elevation-specific changes in temperature and precipitation, indicating diverging phenologies of neighboring communities. Subpopulations of individual species also diverged at mid-elevation but converged in phenology at high elevation. phenology_data: Data on flowering phenology of 590 taxa collected by C. David Bertelsen over 33 years (1984-2016). A total 169,030 observations were recorded during 1,639 surveys. Data were collected along an 8.05-km trail in Finger Rock Canyon ascending from 945-2212 m, to Mt. Kimball in the Santa Catalina Mountains of Arizona, USA. The trail was partitioned into five elevation bands with distinct flowering assemblages (communities) during the growing seasons: 1) 945-1079 m, 2) 1079-1372 m, 3) 1372-1671 m, 4) 1671-1939 m, and 5) 1939-2212 m. Every species seen in anthesis (angiosperms) or releasing pollen (gymnosperms), together referred to as “flowering,” was recorded for each community along each 1.6-km-long trail segment on every survey. temperature_precipitation_data: Temperature and precipitation data for three locations within Finger Rock Canyon in the Santa Catalina Mountains of Arizona, USA. The 1930-2016 Parameter-elevation Regressions on Independent Slopes Model (PRISM) data was downloaded from the PRISM Climate Group, Oregon State University, (http://www.prism.oregonstate.edu/explorer/), created October 25, 2017. The gauge data was collected by C. David Bertelsen.