The distribution of C4 species of the Cyperaceae in North America in relation to climate.

The percent of species of the Cyperaceae possessing the C4 pathway was calculated for twenty-five regions of North America. A stepwise multiple regression analysis was used to determine which climatic variables were most highly correlated with the percent C4 species among the various regions. The square of the mean July minimum daily temperature exhibited the strongest correlation with the transformed percentage of C4 species. It appears that the relationship to climatic variables of the C4 species of the Cyperaceae is similar, but not identical to the relationship previously reported for C4 species of the Gramineae.