Duckweeds have emerged as frontier plants in research, food, and bioenergy applications. Consistency in genetic and morphological traits within species is therefore crucial for their effective use. Thailand hosts diverse duckweed populations with representatives from four of the five genera and at least four species recorded. However, the extent of genetic and morphological variation within these species in Thailand remains unclear. Here, we investigated the genetic and morphological variation in four duckweed species—Landoltia punctata, Lemna aequinoctialis, Spirodela polyrhiza, and Wolffia globosa—collected from 26 sites across Thailand. Using the multilocus sequence typing approach based on three chloroplast genes (rbcL, atpF–atpH, and psbK–psbI), we show that genetic variation in duckweed is distinct at both inter-species and intra-species levels. Among these four species, Lemna aequinoctialis exhibits the highest genetic variation, forming four distinct phylogenetic clusters. This is followed by Spirodela polyrhiza, Wolffia globosa, and Landoltia punctata. In addition, we observe that morphological variation, particularly frond aspect ratio, varies significantly among clusters but remains consistent within each cluster of each species. These findings suggest that duckweed populations in Thailand exhibit substantial genetic variation at the intraspecific level, which is closely associated with frond morphological variation.

Duckweed has attracted considerable attention for its high protein content, rapid growth, and broad potential in biotechnological applications. Understanding key phenotypic traits is crucial for unlocking and maximizing this potential. While most studies on duckweed growth have been conducted under natural or non-sterile conditions, here we minimize environmental influences and focus on the genetic component of growth by assessing growth performance under axenic culture. In this study, we measured relative growth rate (RGR) in four duckweed species, Landoltia punctata (G. Mey.) Les & D. J. Crawford, Lemna aequinoctialis Welw., Spirodela polyrhiza (L.) Schleid., and Wolffia globosa (Roxb.) Hartog & Plas. collected from various natural locations across Thailand. A total of six to seven strains were tested for each species. The relative growth rates of studied species ranged from 0.012 day⁻¹ in S. polyrhiza to 0.162 day⁻¹ in W. globosa. Significant intraspecific variation was observed in L. punctata, S. polyrhiza, and W. globosa, with the coefficients of variation between 9.6 to 109.9 percent. Each strain showed distinct growth characteristics: Most displayed a steady growth pattern, whereas W. globosa showed exponential growth at Day 35 after the start of experiment. The results provide the first systematic comparisons of baseline growth rate data for duckweed species in Thailand. These findings advance the understanding of strain-specific growth traits in duckweed and establish a standardized protocol for evaluating growth traits under axenic conditions, providing a basis for future research and applications.