Background: Natural hybridization in plants is a vital mechanism of speciation. Calanthe arisanensis and C. sieboldii occur in the same habitat in northern Taiwan, where there are a number of plants whose morphologically characters are similar in between of these two species. In this report, a new natural hybrid, Calanthe species - C. xhsinchuensis Y.I. Lee putatively derived from the natural hybridization of C. arisanensis and C. sieboldii was described and illustrated. Besides, somatic chromosome number was counted.
Results: The morphological and histological data of flowers, capsules, roots and leaves of C. xhsinchuensis show an intermediate condition between its putative parents. The chromosome number, 2n = 40, is also congruent with its putative parents. Color plates and line drawings are provided to aid in identification.
Conclusion: Base on the morphological characteristics of reproductive and vegetative organs, and the distributions of putative parents, it is proposed that C. xhsinchuensis is a natural hybrid between C. arisanensis Hayata and C. sieboldii Decaisne ex Regel.
Keywords: Calanthe; Calanthe arisanensis; Calanthe sieboldii; Calanthe xhsinchuensis; Chromosome number; Natural hybrid; Orchidaceae; Taiwan.