There is evidence that broad-scale species richness patterns of woody plants correlate with contemporary gradients of environmental energy inputs and water availability. However, climate-richness relationships for herbaceous species are less well known. Here we analyze the seed-bearing flora of Great Britain, quantifying the relationships between total, herb, and woody plant species richness and 14 environmental predictors measuring levels of energy, water, or combined energy and water. PCAs of the environmental variables identified the primary trends of environmental variation across Great Britain related to mean annual temperature and annual precipitation. OLS multiple regression and partial regression analyses identified mean annual temperature as the strongest driver of richness for all species groups. Similarly, reparameterized versions of published energy—water models for woody plant species richness and for angiosperm family richness gradients also identified energy variables as the primary predictors of the richness of all, woody, and herb species.