4.4 | Hybrid speciation
Hybridization was increasingly recognized as an important component of species evolution (Mallet, 2005; Mallet et al., 2016; Stukenbrock, 2016). New species were produced by different ways of evolution, such as polyploidization, homoploid hybridization, and introgressive hybridization (Rieseberg & Carney, 1998; Wang, 2017). Due to the abundant genetic and phenotypic variation in the hybrid progeny population, the boundaries between them and their parents became blurred and difficult to distinguish (Abbott, 2003). Therefore, in the past, botanists only defined a new species according to morphological characteristics, which was easy to lead to the wrong understanding of species. In other words, some previously published species were likely to be hybrid or intermediate state of hybrid transition to new species. For example, in the Triticeae, Zeng (2011) through cytology and DNA sequence analysis showed that Kengyilia stenachyra is a natural hybrid of K. rigidula and Elymus nutans , rather than a real species. Hybrid progeny population was highly variable, which retained the important transition types in the evolution process, and was an indispensable part of the material system to explore the formation mechanism of hybrid speciation (Rieseberg, 1997). So, the natural hybrids found in this study provided a good research material for exploring the formation. Further research will be needed on the formation of hybrid species.