LAUSR

Aim: Phylogenetic structure of regional species assemblages is determined by environmental conditions and biogeographical history. Typically, assemblages are thought to become increasingly clustered at higher latitudes, because relatively few clades can tolerate low temperatures. However, numerous other patterns can produce phylogenetic structure. Here, we derive and test four hypotheses for phylogenetic structure of all angiosperms and five major angiosperm clades in North America. These are as follows: (a) angiosperms assemblages at higher latitudes are more phylogenetically clustered; (b) stronger phylogenetic clustering occurs in the drier climates of the west; (c) species are more closely related in the warm, dry southwest than in the cooler, wetter northwest; and (d) latitudinal patterns of phylogenetic structure in central North America are intermediate between those of the east and west.