Growth dynamics of a clonal plant population would be different depending on the number of gents that consists of the population. Therefore, the population yields of rhizomes were experimentally compared between the populations composed by a single genet and those by multi-genets.

Rhizomes of four genets of Fallopia japonica were collected at the riverbank of the river Tamagawa in March 2010. Rhizomes with 10cm long were planted in a 50 cm * 50 cm 8 15cm plastic box. There were two rhizome density treatments (four rhizomes and eight rhizomes in a box) and three genet-structure treatments (single genet, two genets, and four genet in a box) with 16 replicates. Plants of 7 replicates were harvested in December 2010 and 9 replicates in December 2011.

In both years, there were marginally significant differences in rhizome biomass between the genet-structure treatments. In the four-rhizomes treatments, rhizome biomass increased with the number of genets. In 2011, there were significant differences in rhizome biomass between the rhizome density treatments but not in 2010.

The genet structure in a population of a clonal plant affected its rhizome biomass. A clonal plant may utilize its environment more ‘comprehensively’ under the existence of multi-genets because each genet has a potentially different niche.