| Summary: | 碩士 === 國立臺灣大學 === 森林環境暨資源學研究所 === 99 === With only 14 species, Taiwanese begonias are exceptional for their extensive variation in chromosome numbers (2n=22, 26, 36, 38, 52, 60, 64, 82), implying that mechanisms such as interspecific hybridization, polyploidization, and subsequent aneuploidization should have been crucial in generating the diversity of begonias in Taiwan. To untangle the origins of Taiwanese begonias and their complicated evolutionary history, DNA sequences of two low-copy nuclear genes (PI, RPB2) and cpDNA intergenic spacers (trnL-trnF, trnC-ycf6, and accD-psaI) of Taiwanese and representative begonias from adjacent Asian regions were analyzed. The nuclear gene trees and cpDNA trees all support that B. ravenii (sect. Diploclinium) and B. fenicis (sect. Diploclinium) are two distinct species and belong to different clades of sect. Diploclinium.
Based on cpDNA and nuclear gene trees, we hypothesize the following：Four putative diploid progenitors probably had involved in the formation of Taiwanese endemic polyploid begonias, as suggested by the four clades (A, B, C, and D) in both nuclear gene trees. With the exception of B. longifolia, the exact identity of the other three putative progenitors remains unclear.
Two 2n=38 groups (B. taiwaniana and Chitoensis group) were formed from A × C and B × D hybrids, respectively, with A and B as maternal progenitors. B. formosana was derived from the hybrid between the progenitor of Chitoensis group (BD) and B. longifolia. The 2n=52 group are hypothesized to have originated from polyploidizations and subsequent aneuploidization between the two 2n=38 groups. Begonia tengchiana (2n=82) might have derived from the hybrids between B. taiwaniana and B. formosana.
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