Molecular confirmation of unidirectional hybridization in Begonia x taipeiensis Peng (Begoniaceae) from Taiwan

An unusual Begonia that sheds staminate flowers prematurely at bud stage wa s collected from several localities in northern Taiwan. Observations on mor phology, pollen stainability, and seed set of this species initially sugges ted a hybrid origin. Morphological comparisons, distribution patterns, chro mosome cytology, and experimental hybridization showed that such plants are F-1 hybrids (2n = 41) between Begonia formosana (Hayata) Masamune (n = 30) and B. aptera Blume (n = ii), both of which are widespread in Taiwan and s ympatric in most of their ranges. These hybrids were named Begonia X taipei ensis Peng. Experimental crosses between the putative parental species cons istently resulted in germinable seeds and healthy F-1 plants only when B. f ormosana was used as the female parent. Molecular data obtained from sequen ces of the atpB-rbcL spacer of chloroplast DNA confirmed that unidirectiona l hybridization between the putative parents in the wild resulted in the fo rmation of B. X taipeiensis. No natural hybrid populations with a maternal origin from B. aptera have been detected. Abortion caused by a post-pollina tion barrier occurs when B. aptera was used as a maternal parent. Low polle n fertility of F-1 hybrids indicates that the natural hybrid is maintained by recurrent hybridization between the parental species.