Background: In the past several millenniums, we have domesticated several crop species that are crucial for human civilization, which is a symbol of significant human influence on plant evolution. A pressing question to address is if plant diversity will increase or decrease in this warming world since contradictory pieces of evidence exit of accelerating plant speciation and plant extinction in the Anthropocene. Results: Comparison may be made of the Anthropocene with the past geological times characterised by a warming climate, e.g., the Palaeocene-Eocene Thermal Maximum (PETM) 55.8 million years ago (Mya)—a period of “crocodiles in the Arctic”, during which plants saw accelerated speciation through autopolyploid speciation. Three accelerators of plant speciation were reasonably identified in the Anthropocene, including cities, polar regions and botanical gardens where new plant species might be accelerating formed through autopolyploid speciation and hybridization. Conclusions: However, this kind of positive effect of climate warming on new plant species formation would be thoroughly offset by direct and indirect intensive human exploitation and human disturbances that cause habitat loss, deforestation, land use change, climate change, and pollution, thus leading to higher extinction risk than speciation in the Anthropocene. At last, four research directions are proposed to deepen our understanding of how plant traits affect speciation and extinction, why we need to make good use of polar regions to study the mechanisms of dispersion and invasion, how to maximize the conservation of plant genetics, species, and diverse landscapes and ecosystems and a holistic perspective on plant speciation and extinction is needed to integrate spatiotemporally.