The world’s diverse and complex climates pose significant challenges in ecological and evolutionary studies, frequently resulting in climatic characterizations that overlook the significance of transitional climates. This study examines the nature and distribution of the transitions between climatic regions worldwide and evaluates their impact for inferring the past and present climatic preferences of the Asian Palmates, a highly diverse and climatically complex lineage of Araliaceae. We find consistent geographic patterns of transitions worldwide and extraordinarily heterogeneous climates in the transitions between the temperate and tropical climates in Eurasia. Notably, many current genera of the Asian Palmates and their early ancestors have strong affinities for transitional zones, suggesting an initial diversification under such climates. Such results emphasize the significance of transitional climates in understanding niche diversity and evolutionary patterns and calls for a (re)evaluation of the role of transitional areas in promoting biodiversity across the Tree of Life.

Cissus is the largest genus in Vitaceae and is mainly distributed in the tropics and subtropics. Crassulacean acid metabolism (CAM), a photosynthetic adaptation for the occurrence of succulent leaves or stems, indicates that convergent evolution occurred in response to drought stress during species radiation. Here, we provided the chromosomal level assembly of Cissus rotundifolia (an endemic species in Eastern Africa) and genome-wide comparison with grape to understand genome divergence within an ancient eudicot family. Extensive transcriptome data were produced to illustrate the genetics underpinning C. rotundifolia’s ecological adaption to seasonal aridity. The modern karyotype and smaller genome of C. rotundifolia (n = 12, 350.69 Mb/1C), which lack further whole-genome duplication, were mainly derived from gross chromosomal rearrangement such as fusions and segmental duplications, whilst sculpted by a very recent burst of retrotransposons activity. Bias on local gene amplification contributed to its remarkable functional divergence with grape and the specific proliferated genes associated with abiotic and biotic responses (e.g., HSP-20, NBS-LRR) enabled C. rotundifolia to survive in a hostile environment. Re-organization of existing enzymes of CAM characterized as diurnal expression patterns of relevant genes further confer to its present thriver in dry savannas.