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Background  Our aim is to understand the evolution of species-rich plant groups that shifted from tropical into cold/temperate biomes. It is well known that climate affects evolutionary processes, such as how fast species diversify, species range shifts, and species distributions. Many plant lineages may have gone extinct in the Northern Hemisphere due to Late Eocene climate cooling, while some tropical lineages may have adapted to temperate conditions and radiated; the hyper-diverse and geographically widespread genus  Hypericum  is one of these.    Results  To investigate the effect of macroecological niche shifts on evolutionary success we combine historical biogeography with analyses of diversification dynamics and climatic niche shifts in a phylogenetic framework.  Hypericum  evolved cold tolerance  c.  30 million years ago, and successfully colonized all ice-free continents, where today ~500 species exist. The other members of Hypericaceae stayed in their tropical habitats and evolved into ~120 species. We identified a 15–20 million year lag between the initial change in temperature preference in  Hypericum  and subsequent diversification rate shifts in the Miocene.    Conclusions  Contrary to the dramatic niche shift early in the evolution of  Hypericum  most extant species occur in temperate climates including high elevations in the tropics. These cold/temperate niches are a distinctive characteristic of  Hypericum . We conclude that the initial release from an evolutionary constraint (from tropical to temperate climates) is an important novelty in  Hypericum . However, the initial shift in the adaptive landscape into colder climates appears to be a precondition, and may not be directly related to increased diversification rates. Instead, subsequent events of mountain formation and further climate cooling may better explain distribution patterns and species-richness in  Hypericum . These findings exemplify important macroevolutionary patterns of plant diversification during large-scale global climate change.    Electronic supplementary material  The online version of this article (doi:10.1186/s12862-015-0359-4) contains supplementary material, which is available to authorized users.

Oligocene niche shift, Miocene diversification – cold tolerance and accelerated speciation rates in the St. John’s Worts (Hypericum, Hypericaceae)