Data from: Spatial phylogenetics of the North American flora

North America is a large continent with extensive climatic, geological,
soil, and biological diversity. That biota is under threat from habitat
destruction and climate change, making a quantitative assessment of
biodiversity of critical importance. Rapid digitization of plant specimen
records and accumulation of DNA sequence data enable a much-needed broad
synthesis of species occurrences with phylogenetic data. Here we attempted
the first such synthesis of a flora from such a large and diverse part of
the world: all seed plants for the North American continent (here defined
to include Canada, United States, and Mexico) with a focus on examining
phylogenetic diversity and endemism. We collected digitized plant specimen
records and chose a coarse grain for analysis, recognizing that this grain
is currently necessary for reasonable completeness per sampling unit. We
found that raw richness and endemism patterns largely support previous
hypotheses of biodiversity hotspots. Application of phylogenetic metrics
and a randomization test revealed novel results, including significant
phylogenetic clustering across the continent, a striking east-west
geographic difference in the distribution of branch lengths, and the
discovery of centers of neo- and paleo-endemism in Mexico, the
southwestern USA, and the southeastern USA. Finally, our examination of
phylogenetic beta-diversity provides a new approach to comparing centers
of endemism. We discuss the empirical challenges of working at the
continental scale, and the need for more sampling across large parts of
the continent, for both DNA data for terminal taxa and spatial data for
poorly understood regions, to confirm and extend these results.