Hybrid between Lemna minor and L. turionifera (L. × japonica, Lemnaceae) in East Europe is more frequent than parental species and poorly distinguishable from them

Abstract

Biodiversity studies and practical use of duckweeds are impossible without reliable species identification. Despite of clear genetic differentiation of L. minor, L. turionifera and their hybrid L. × japonica, their morphological discrimination is challenging even for professional botanists; consequently, the distribution of the two latter taxa is not precisely known. Although numerous determination keys exist, none of them is based on quantitative analysis of the morphological variation observed in nature. Thus, we aimed to study variation of morphological characteristics most frequently proposed for discrimination between L. minor, L. turionifera and L. × japonica (frond shape and pigmentation, papule presence along the median nerve) on specimens collected in the wild, which were taxonomically identified using molecular tools (intron length polymorphism in the β-tubulin gene). We focused on samples from the poorly studied East Europe, including some from the Russian Far East for comparison. Lemna × japonica appeared to be quite abundant in different regions of East Europe. The Far Eastern occurrences of L. minor and L. × japonica should be carefully verified. Even our limited sampling demonstrated that morphological characters conventionally used for delimitation of L. minor, L. turionifera and L. × japonica do not work in wild populations. Additional studies should be performed for verification of diagnostic value of generative characters. Large-scale genetic screening of Lemna populations in nature is also indispensable to clarify distribution of taxa from the L. minor complex.