Geographical Variation in Seed Weight of Plantago asiatica L.

概要

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Planlago asiatica L. consists of two ecotypes : the northern ecotype and the southern one. The two ecotypes showed different patterns of correlations between seed weight and a geographical or thermal gradient. The mean seed weight of the southern-ecotype populations increased within 25-37°N of the latitude and decreased with the cumulative temperature ; that of the northern-ecotype populations decreased within 38-45°N of the latitude and increased with the cumulative temperature. It seems that the preference of seed number is not so important to the southern-ecotype populations.Rather, the southern-ecotype populations at higher latitudes prefer to the strategy by which individuals produce heavier seeds at the expense of seed number, allowing germinated plants to grow and reproduce with advantage under a shorter growing season. As a result, the strategy seems to be reflected in the latitudinal pattern in the field. The northern ecotype is considered to have a propagation strategy by which small amounts of assimilated resources, restricted by the severe environments, are used to ensure seed number at the expense of seed weight. The results in the present study suggest the possibility of this idea. Key word : Distribution, ecotype, geographical variation, Plantagp asiatica L., seed weight.
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