Chemotaxonomic and cytogenetic studies on Perilla frutescens var. citriodora ('Lemon Egoma')

Chemical analysis of the essential oils of 29 strains of Perilla frutescens Britton var. citriodora (Makino) Ohwi growing wild in various regions of Japan showed that citral, a fragrance component, which had been considered an important taxonomic character of this varietas, was not necessarily a major characteristic component of this variety: in 7 strains, another substance, such as naginata-ketone, isoegomaketone or elemicin was the major essential component. Cytological examination revealed that var. citriodora has only 20 chromosomes, whereas both var. acuta Kudo and var. japonica Hara have 40 chromosomes. The F₁ hybrid between citriodora and acuta, occasionally obtained by artificial crossing, was found to be sterile, bearing no seed. In the meiosis of the F₁ plant, 10 bivalent and 10 univalent chromosomes were observed, suggesting that acuta and japonica are allotetraploids (AABB) having one genome in common with citriodora (AA). It is proposed on the basis of these results that citriodora should be regarded as an independent species different from P. frutescens.