Genetic relationships and polyploid origins in the Lippia alba complex

Abstract

Premise Plant genomes vary in size and complexity due in part to polyploidization. Latitudinal analyses of polyploidy are biased toward floras of temperate regions, with much less research done in the tropics. Lippia alba has been described as a tropical polyploid complex with diploid, triploid, tetraploid, and hexaploid accessions. However, no data regarding relationships among the ploidal levels and their origins have been reported. Our goals are to clarify the relationships among accessions of Lippia alba and the origins of each ploidal level. Methods We investigated 98 samples representing all five geographical regions of Brazil and all ploidal levels using microsatellite (SSR) allelic variation and DNA sequences of ITS and trnL‐F. Nine morphological structures were analyzed from 33 herbarium samples, and the chemical compounds of 78 accessions were analyzed by GC–MS. Results Genetic distance analysis, the alignment block pattern, as well as RAxML and Bayesian trees showed that accessions grouped by ploidal level. The triploids form a well‐defined group that originated from a single group of diploids. The tetraploids and hexaploid grouped together in SSR and trnL‐F analyses. The recovered groups agree with chemical data and morphology. Conclusions The accessions grouped by ploidal level. Only one origin of triploids from a single group of diploids was observed. The tetraploid origin is uncertain; however, it appears to have contributed to the origin of the hexaploid. This framework reveals linkages among the ploidal levels, providing new insights into the evolution of a polyploid complex of tropical plants.

Chemistry of essential oils of the shrub Lippia alba (Verbenaceae) from Mexico and Costa Rica

“…There is natural polyploidy within the species, a mechanism of plant speciation that results in morphological plasticity and the presence of several chemotypes (Reis et al, 2014). Lopes et al (2020) studied genetic relationships and polyploid origins in the L. alba complex, and they found that there is an association between morphological characters and ploidal level but the patterns of genetic and chemical variation are not related to geographical distribution. Biotypes found in the subtropical regions of America (both in the north and in the south) are characterized by pendulous branches, and it is assumed that this feature is a response to periods of low temperatures.…”