Reproductive mode of Polygonum viviparum depends on environment

We investigated the effects of microenvironmental conditions on the reproductive characteristics of Polygonum viviparum in the Southern Alps of Japan. We examined environmental differences and the distribution of P. viviparum at four study sites on the southeast-facing cirque of Mt Maedake. P. viviparum was found at two sites, where the humic loam layer was well developed on the soil surface. The timing of snowmelt differed considerably between these two sites. On average, the ratio of flowers to bulbils per inflorescence was low and the production of bulbils was high in the population experiencing later snowmelt. The mean maximum leaf area, number of flowers per inflorescence, and fresh weight of bulbils decreased with decreasing length of the growing season. In contrast, the number of individuals without inflorescences increased with decreasing length of the growing season. The starch content of the rhizomes of each individual was similar, regardless of the presence of flowers in the inflorescence. Within rhizomes, the starch content in the old rhizome was lower than that in the new and central portions of the rhizome. The starch content of the old rhizome was higher in individuals without inflorescences; starch appeared to be consumed for inflorescence production.