A note on phenology and seed-germination behavior in two natural populations of the endangered aquatic macrophytes, Sparganium erectum var. erectum and S. erectum var. macrocarpum (Sparganiaceae).
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概要
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Annual fluctuation of the phenological features and seed-germination behavior in two natural populations of Sparganium erectum L. var. erectum and var. macrocarpum Hara, in the Kinki district, Japan were monthly monitored from July, 1999 to November, 2000, and seeds from natural populations were examined by pericarp removal and a gradually increasing and decreasing temperature method (GT method). Two varieties showed a standard phenological pattern as summer green perennials. They emerged as above-ground juveniles in spring, bore flowering inflorescences in July, disseminated fruits in late summer to autumn, and withered aboveground shoots in winter. Plants of S. erectum var. erectum bore many flowering shoots in summer and disseminated seeds and/or ramets with disturbance of its natural habitats by flood caused by typhoon and/or with normal seed disseminations. Its seedlings naturally emerged in spring and autumn with wide annual fluctuations. Plants of S. erectum var. macrocarpum showed a low rate of flowering shoots compared with that of var. erectum, and no seedlings were found in the natural habitat after seed dissemination. The seeds of two varieties showed a similar primary dormancy immediately after dissemination. The seeds which excised their pericarps broke dormancy one year later. The GT method indicated that seeds of var. erectum required more temperature fluctuation than those of var. macrocarpum, suggesting adaptation of germinating behavior to a particular season. Our results suggested that var. erectum has a life history trait adaptable to the disturbed habitat near a river and var. macrocarpum to a relatively stable environment such as a pond with stable water.
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