Life history characteristic ofCyrtomium falcatum around the natural northern boundary in Hokkaido,with reference to the alternation of generations

To understand the life history characteristic for expanding the distributional area to colder climates, developmental age structure of population ofCyrtomium falcatum was observed along southwestern coasts of Hokkaido at the natural northern boundary of its distribution, with reference to the alternation of generations. The length and number of pinna of fertile leaves ofCyrtomium falcatum decrease towards the northern part of Japan. In southwestern Hokkaido, typically dwarf fertile leaves and gametophytes were observed growing together on cliffs nearby the sea. To estimate the developmental ages of small and dwarf leaves, the number of venation (NV: branching number of vein from midrib) of leaves was counted on each sporophyte. The sporophyte with leaves at the simple pinna stage ranging from 0–25NV, is predominant in the population of southwestern coasts of Hokkaido. The fertility of the sporophyte seems to be achieved more than five years after the germination. The gametophytes were also observed at the location to be almost equal in number to sporophytes. The number of gametophytes and sporophytes decreases with advancement of developmental stages. In the same location at Okushiri Isl. with slight gradiency of humidity, the gametophyte is predominant on the drier cliff, while the sporophyte is predominant on the humid hole. The population ofCyrtomium falcatum at the natural northern boundary in Hokkaido, seems to have the life history characteristic with alternation of generations. Contribution No. 2557 from the Inst. of Low Temp. Sci.