AbstractFour JapaneseTrillium(Liliaceae) species which are representative perennial herbs of the temperate deciduous forests—Trillium kamtschaticum(2x),T. apetalon(4x),T. tschonoskii(4x) andT. smallii(6x)—were studied for their reproductive characteristics, e.g., patterns of reproductive resource allocation and reproductive output.In spite of the differences in ploidy levels (from 2x to 6x), all four species showed very similar reproductive traits. It became evident that in response to the increase in reproductive allocation to total reproductive organs (RA), the number of seeds produced per plant (PN) clearly increased. This trend is well in accord with the relationship found in four North American species and also several temperate woodland perennial herbs which occur in closed, stable and predictable environments, and possess typical xenogamous breeding systems. Although there is no conspicuous trend between ploidy levels and PN, one of the significant differences noted in this study was in seed weight, which ranged from 2.93 mg in diploids, to 3.42–3.45 mg in tetraploids, and to 4.47 mg in hexap