Comparative characterization of two closely related achlorophyllous orchids, Gastrodia nipponica and G. tokaraensis
2006
Umata, H.(Kagoshima Univ. (Japan). Faculty of Agriculture) | Yokota, M.
Investigated were characteristics of the two achlorophyllous myco-heterotrophic orchids, Gastrodia nipponica and a closely related species G. tokaraensis. The latter species was reported as a new species by the authors recently. The two orchids inhabit the bamboo forest on the island of Takeshima, the northernmost island of the Ryukyu Islands of Japan. There are great differences between the two orchids in morphology and ecology. The conspicuous characteristics of G. nipponica are its scattered emergence usually on thickly fallen bamboo leaves, the short lived and simple root system, and the short-lived pubescent rhizomes in the F-layer in soil forming the monopodial or sympodial rhizome system. In contrast, G. tokaraensis emerges gregariously in a colony about 70 cm in diameter in open spaces or soil by paths in bamboo forests; it has the perennial and large complex root system, and the perennial smooth rhizomes in the A-layer in soil forming the large rhizome network system in a colony about 70 cm in diameter. In addition, the embryo volume of G. tokaraensis is less than half of that of G. nipponica. It was also observed that the G. tokaraensis plants and the flowers drastically decreased in number only for a two-week period. Similarities observed in both orchids are as follows: the two orchids flower and fruit from mid-April to the latter half of May, however G. tokaraensis emerges at least two weeks later than G. nipponica. Both orchids can propagate from the rhizomes. The habit of the emergence above ground reflects the rhizome system in the ground of the orchid. And it is suggested that there is a close relationship between the rhizome surface and the underground location of the rhizome.
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