Ploidy level and their relationship with vegetative traits of mulberry (Morus spp.) species in Taiwan

•The unfolded young leaves exhibited the best maturity for determining DNA content and ploidy levels.•Two triploid accessions were identified whereas the rest were diploids.•Triploid accessions have morphologically larger than the diploids accessions.•Lengths of internodes can serve as a quick index checking polyploidy in the field.