Lineage diversity can refer to the number of genetic lineages within species or to the number of deeper evolutionary lineages, such as genera or families, within a community. Community lineage diversity (CLD) is of interest to ecologists, evolutionary biologists, biogeographers, and those setting conservation priorities. Despite its relevance, it is not clear how to best quantify CLD. With North American tree communities as an example, we test which taxonomic and phylogenetic metrics best measure CLD. We find that phylogenetic metrics outperform taxonomic metrics. Faith’s phylogenetic diversity performs well, but is skewed towards the number of lineages in recent time. The best metric is newly derived here, and termed time integrated lineage diversity (TILD). Mapping the lineage diversity of tree communities across the contiguous United States, we find a spatial pattern differing from that of species richness in key areas. The Pacific Northwest, Great Lakes Region, state of Maine, and south-eastern piedmont and coastal plain forests all emerge as areas high in lineage diversity, but relatively lower in species richness. We urge the consideration of lineage diversity, as well as species richness, when setting conservation priorities.