Figure 6 . Summary of climatic niches and elevational distributions of Climatically-Similar Non-Alpine (CSNA) species, defined here as non-alpine species whose ranges encompassed the same temperature and precipitation conditions as alpine taxa. (a ) Phylogeny of alpine (blue tips ) and CSNA (brown tips ) species. At this broad scale, no clear phylogenetic separation of the two groups exists, and both groups are distributed broadly across the seed plant phylogeny. However, at the genus level, substantial taxonomic differences were observed, and these differences persisted at both the familial and ordinal levels (see Table 1 and main text). (b-c ) Density histograms of the occupied climatic niche space and niche breadth, respectively, of CSNA species, showing good overlap between their climatic conditions and those of true alpine species (compare with panels d in Fig. 2-3). (d ) Elevational distribution of CSNA (brown bars ), compared to the elevational distribution of all species in our dataset (“All Sp.”, grey bars ). Compared with the American seed plant species pool overall, CSNA species tended to have ranges that included a higher proportion of mountain foothills (with frost exposure) and, to a lesser extent, lower montane, habitat. Additionally, a lower proportion of their ranges were found in exclusively frost-free or lowland areas. (Up. Mon: upper montane; Lw. Mon.: lower montane; alpine elevational categories omitted here for clarity. ) (e ) Scatterplot showing a strong (R2=0.68) and significant (p<0.001) positive correlation between species richness at Mexican sites where alpine richness was lowest and CSNA richness was highest, indicating that sites which support higher richness for one group likely do so for the other group was well.