Some annual flowering plants have evolved to have very short life histories, the record being less than three weeks from germination to seed set. The annual life strategy may offer advantages of being able to survive drought, heat, frost and other unfavourable periods as seeds. The present paper presents a comparative study of perennials and annuals, and examines morphological trends and climatic factors that might favour annuality. Using a combination of genetic information, trait data and GBIF-mediated occurrences of 80 Veronica species, researchers found significant differences between the two strategies, as perennials had larger leaves, petals and stamina, and annuals had larger bracts. In terms of climatic trends, annual habitats had higher temperatures, but perennial habitats were generally wetter. All examined annual species of Veronica originated in the Mediterranean and southwest Asia, likely because of parallel evolution spurred by aridification.
Wang J-C, Pan B-R and Albach DC (2016) Evolution of morphological and climatic adaptations in Veronica L.(Plantaginaceae). PeerJ. PeerJ 4: e2333. Available at doi:10.7717/peerj.2333.