李建华1,Zhihua JIAO2
Jianhua LI1,Zhihua JIAO2
摘要： Pachysandra is an eastern Asian-North American disjunct genus with three species, two in eastern Asia (P. axillaris and P. terminalis) and one in eastern North America (P. procumbens). While morphological and cytological studies suggest a close affinity of P. procumbens with P. axillaris, molecular data from nuclear and chloroplast DNA regions have provided conflicting signals. In this study, we tested previous phylogenetic hypotheses using sequences of nrDNA ITS and chloroplast ndhF gene from multiple individuals of each of the three species. We also estimated the time of divergence between eastern Asia and eastern North America. Our results support the morphological and cytological conclusion that P. procumbens is more closely related to P. axillaris than to P. terminalis. The phylogenetic congruence of nuclear and chloroplast sequence data suggests that P. terminalis may be an autopolyploid species. The estimated time of divergence of P. axillaris and P. procumbens was 14.6 5.5 mya, which is consistent with estimates from many other eastern Asian-North American disjunct genera. The migration of Pachysandra populations from eastern Asia to North America may have occurred via the North Atlantic land bridge.
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