Among the World’s most challenging environments for plant life is the Atacama Desert, an arid zone extending over 1300 km and from sea level to 2000/3000 m along the southwestern Andean foothills. Plants there and in the adjacent Mediterranean zone exhibit striking adaptations, and we here use a species-rich such group to address the question whether adaptations arose in parallel, at different times, or simultaneously. Answering this type of question has been a major concern of evolutionary biology over the past few years, with a growing consensus that lineages tend to be conservative in their vegetative traits and niche requirements. Combined nuclear and chloroplast DNA sequences for 112 species of Oxalidales (4900 aligned nucleotides) yielded a fossil-calibrated phylogeny that includes 43 of the 54 species of Oxalis occurring in Chile. Distribution models (SDMs) for these species that included precipitation, temperature, fog and/or vegetation types and the phylogeny were used to reconstruct ancestral habitat preferences, relying on likelihood and Bayesian techniques. Since uneven collecting can reduce the power of SDMs, we used a background sample from 1224 Chilean Oxalis collections to correct models for collecting effort. Models with just 10 of 19 bioclim parameters did as well as more parameter-rich models. Results reveal that the Oxalis flora of Chile consists of seven distant lineages that originated at different times prior to the last Andean uplift pulse and some of which had features pre-adapting them to seasonally arid or xeric conditions. The Mediterranean core zone, south of the Atacama, offered an ecological refuge for insufficiently arid-adapted species and harbors a mix of ancient and young groups. There is no evidence of rapid adaptive radiation.