Homoploid hybridization of plants in the Hengduan mountains region.

The Hengduan Mountains Region (HMR) is a major global biodiversity hotspot. Complex tectonic and historical climatic conditions created opportunities for natural interspecific hybridization. Likewise, anthropogenic disturbance potentially raises the frequency of hybridization. Among species studies to date, the frequency of homoploid hybridization appears in the HMR. Of nine taxa in which natural hybridization has been detected, three groups are involved in homoploid hybrid speciation, and species pairs from the remaining six genera suggest that continuous gene flow occurs in hybrid zones. Reproductive isolation may greatly affect the dynamic and architecture of hybrid zones in the HMR. Asymmetrical hybridization and introgression can primarily be attributed to both prezygotic and postzygotic barriers. The frequent observation of such asymmetry may imply that reproductive barrier contributes to maintaining species boundaries in the alpine region. Ecological isolations with environmental disturbance may promote breeding barriers between parental species and hybrids. Hybrid zones may be an important phase for homoploid hybrid speciation. Hybrid zones potentially provided abundant genetic resources for the diversification of the HMR flora. The ecological and molecular mechanisms of control and mediation for natural hybridization will help biologists to understand the formation of biodiversity in the HMR. More researches from ecological and molecular aspects were required in future studies.