Triploidy is prominent in the duckweed Lemna minor complex

Duckweeds (Lemnaceae Martinov) are aquatic monocotyledonous plants known to be the smallest and fastest-growing flowering plants on Earth. Many species are morphologically indistinguishable due to their reduced structures, yet molecular evidence suggests that visually similar clones could be distinct species or hybrids. Using a comprehensive suite of genomic, molecular and cytogenetic methods, we analyzed 58 presumed Lemna minor clones to resolve their relationships. Our study revealed extensive genome plasticity within the "Lemna minor complex," identifying diploid and triploid L. minor clones, as well as allodiploid and allotriploid interspecific hybrids, in addition to a novel African-clade L. minor lineage. Triploidy in the L. minor complex is prevalent in nature, occurring in 33% of the clones previously identified as L. minor in our collection, and is associated with enhanced growth metrics under optimal conditions. For asexually propagative species such as duckweeds, where the triploid block is not a deterrent, triploid progenies may become the majority as has been observed in numerous wild Lemna populations. Our study shows that polyploidy and hybridization in these primarily asexually propagating plants could play important roles in their population dynamics and evolution under changing environments.