Cytomorphological Studies in the Genus <i>Spiranthes</i> Rich

The allopolyploid origin ofSpiranthes hongkongensis(Orchidaceae)

“…Chromosome counting-s-Ytie chromosome numbers of S. sinensis and S. spiralis have been reported by several authors to be 2n = 30 (e.g., Hagerup, 1944;Tanaka, 1969;Vij and Vohra, 1974). Thus in the present study, chromosome counting was conducted for only S. hongkongensis.…”

“…Duration of anthesis in S. sinensis at any locality is =4-5 wk, while populations of S. hongkongensis usually finish flowering within 3 wk. The flowering period of S. spiralis is from April (at elevations 600-650 m) to May (at elevation 800 m) in the Himalayas area (Vij and Vohra, 1974) and from September to November in England (Wells, 1981). The difference in flowering phenology between disjunct populations of S. spiralis is apparently due to the difference in elevation and latitude.…”

“…Chromosomal evidence of polyploidy-Two distinctive cytological series of species are known in the genus Spiranthes: a large group with chromosome numbers based on 15, and a small group with numbers based on 22 (Sheviak, 1990). The chromosome numbers of S. sinensis and S. spiralis have been reported by several authors to be 2n = 30 (e.g., Hagerup, 1944;Tanaka, 1969;Vij and Vohra, 1974), indicating that they belong to the former group. Thus, a chromosome count of :=::60 in S. hongkongensis indicates that the species is a tetraploid.…”

“…The absence of multivalents at meiosis in the plants suggests an allopolyploid origin (Stebbins, 1947). The polyploid plants overlapped in their morphological features with the diploid S. sinensis, and the two cytotypes were often found growing side by side in the area (Vij and Vohra, 1974). Although a hypothetical origin of S. hongkongensis in the Himalayas seems congruent with the known present-day overlap of S. sinensis and S. spiralis, it should be noted that plant distributions have changed drastically during and since the Pleistocene, and the region of overlap between the two diploids could historically have been larger or covered a different area (R.…”

“…Geographical origin of S. hongkongensis-Although S. hongkongensis was described and named in Hong Kong (Hu and Barretto, 1975), it probably originated elsewhere, since S. spiralis is primarily a European species and can be found only in the Himalayan area in Asia. The occurrence of allotetraploid populations in the Himalayan area has been reported, and were considered as cytotype II (4n = 47= 60) of S. sinensis by Vij and Vohra (1974). The authors observed 30 bivalents at metaphase I and unequivocal distribution of 30 chromosomes at each pole at Anaphase I and Anaphase II during meiosis.…”