Analysis of unidirectional hybridization between supra-annual flowering species, Strobilanthes glandulifera, and annual flowering species, S.tashiroi

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In the Motobu Peninsula of Okinawa Island, the present situation of Strobilanthes tashiroi, S.flexicaulis and their putative hybrids are observed and examined ecologically, morphologically and genetically. Ecologically, S.tashiroi and S.flexicaulis in the Motobu Peninsula are confirmed to be polycarpic perennial and monocarpic and periodical mass-flowering species, respectively. The putative hybrids, including F1, F2…and following back-cross generations are also confirmed to derive from hybridization between S.tashiroi and S.flexicaulis with the latter species as major pollen donor. As the pollinators were scarcely found in non-mass-flowering years, it is deduced that hybridization occurs only in the mass-flowering years when the flowers of S. flexicaulis are overwhelming so that the S.flexicaulis acts as major pollen donor in any level of hybridization. Isolation has not been established at least between the hybrids and S.flexicaulis.