The present series of notes, chiefly distributional, have accumulated during several years of plant collecting in the southwestern United States and northwestern Mexico. To these, based on the authors' collections, are added a few notes from certain collections of others received chiefly in exchange. Of the range extensions noted, perhaps some of those included for Mexico are of little phytogeographic importance, but since floras are, and probably will be for some time to come, written on the basis of political boundaries, such notes seemed worth recording. The citation of original place of publication is given for species new to a region or otherwise unfamiliar. Genera are arranged alphabetically within families, except in the Compositae where they are primarily grouped by tribes.