Ecological aspects of desert vegetation in relation to a moisture gradient of an ephemeral stream in central Arizona were investigated. The stream channel, flood plain and north, west, south, east facing slopes represent a moisture gradient going from most mesic to most xeric conditions. In parts of the system, vegetation from the stream channel intergraded into flood plain vegetation which in turn intergraded into slope vegetation types. In other areas there are sharp delineations between stream channel and flood plain, and between flood plain and slope. Trees and legumes preferred medium moisture habitats, while forbs, shrubs and succulents preferred the dryer moisture areas. Family groups like the Compositeae and the Gramineae were found to be distributed ubiquitously. Niche widths were broadest for flood plain species. Diversity was highest on the slopes. Negative correlations between diversity and the Synthetic Stand Moisture Index existed, i.e. as moisture increased diversity decreased. It was postulated that factors other than moisture, i.e. disturbance also strongly influenced diversity.