Abstract
Extinction threatens many species, yet few factors predict this risk across the plant Tree of Life (ToL). Taxon age is one factor that may associate with extinction if occupancy of geographic and adaptive zones varies with time. Age-dependent occupancy can also influence diversification rates and thus extinction risk where new taxa have small range and population sizes. Here we found that faster diversifying plant genera had more species threatened by extinction across the ToL. Evolutionary age had no effect in 297 sampled genera, potentially because they were older, on average, than expected. Repeating our analyses in two large, well-sampled groups, we found that extinction risk decreased with evolutionary age in conifer species but not palms. Range filling increased in older, non-threatened conifers more strongly than in threatened taxa. Our results suggest contrasting modes of speciation may explain differing patterns of extinction risk across the ToL with consequences for biodiversity conservation.