I mentioned in a previous Cercis entry a couple years ago about regretting not photographing Cercis occidentalis while in northern California, so I made sure to do so on this past trip.
Western redbud is native to southwest USA, including California, Arizona, Nevada and Utah. Like other Cercis species, it exhibits cauliflory, i.e., flowers emerge from the woody tissue of branches and stems (see previous entry for additional links on this phenomenon).
Despite there being two Cercis species in North America (the other being the eastern North American Cercis canadensis), these two taxa are not as closely related to each other as Cercis canadensis is to Cercis siliquastrum, a native of southern Europe and western Asia. An examination of the evolutionary relationships and biogeography within Cercis was done by Charles C. Davis et al. in 2002 (Phylogeny and Biogeography of Cercis (Fabaceae): Evidence from Nuclear Ribosomal ITS and Chloroplast ndhF Sequence Data in Systematic Botany 27(2):289-302). The precise reason for the close relationship between Cercis canadensis (a species of temperate climates) and Cercis siliquastrum (a species of dry Mediterranean climates) remains unknown, but most theories suggest a common arid-growing ancestor with later evolution in the Cercis canadensis lineage to become the temperate climate species observed today.