Population biology of Pogonia japonica in Russia and Japan

Pogonia japonica (Orchidaceae) is a clonal plant forming numerous adventitious shoots on long perennial roots. Seeds remained dormant for 3 years or more and rarely germinated. Populations consisted of ramets of different ages. Each ramet was a partial shoot growing vertically and monopodially before changing to sympodial growth after the first flowering. Annual growth consisted of two internodes making it easy to determine the shoot age. Three to 12 ramets were connected by a common root system. This might provide rapid development of ramets. In favorable habitats, vigorous ramets started flowering in the second or third year, and flowering lasted for another 3-4 years. In unfavorable habitats, preflowering shoot development took 3-5 years, or it died before or just after the first flowering. Ramets remained alive but senescent for 1-2 years after the last flowering. Disconnection of 2-4-year-old shoots was a normal process of vegetative reproduction. Some isolated mature shoots stayed dormant for 1-2 years. Young shoots disconnected within the first year usually died. Vegetative mature shoots predominated in the Russian populations, whereas young ramets were more numerous in the Japanese populations. The proportion of flowering to vegetative shoots averaged 15%, but reached as high as 55% in one Japanese population. Fruiting was high (80%) in Russian populations, but in some Japanese populations it dropped to zero after all fruits were damaged by insects. Differences in plant size and population structure reflected differences in ecological conditions more than geographic difference.