Morphological and Molecular Characterization of Duckweed (Lemnaceae) in Selected Wetlands and Pond Waters of Tharaka-Nithi- Nithi County, Kenya

Abstract

Duckweeds are aquatic herbs adapted to various geographic and climatic zones, with significant applications in wastewater treatment, animal feeds, biofuel production, and as a culinary ingredient in some Asian countries. In Kenya, including Tharaka-Nithi County, duckweed has attracted the attention of farmers as a feed supplement for livestock. However, commercial extraction poses a threat to the survival of the plant and its ecological roles, necessitating its conservation and the promotion of sustainable utilization. This study aimed at characterizing local duckweed species to understand their taxonomic variation and distribution in Tharaka-Nithi County. One hundred and forty-four samples were collected from selected wetlands and ponds, with GPS coordinates and elevation of sampling points recorded for analysis of their distribution. Morphological features of duckweed were studied, and the DNA was extracted for molecular characterization using DNA barcoding markers. Based on morphological characterization, samples were grouped into nine clones. All nine clones had parallel veins and obovate fronds with rounded apices. Frond symmetry, color, border, and length varied among clones. Morphological data suggested that the clones belonged to the same genus, consistent with previous studies. Further, molecular characterization that was done using RBCL and matK genes successfully confirmed that they were duckweed species. Six RBCL gene amplification products were sequenced, with BLAST search results indicating the genus Lemna. Three samples collected from Chogoria, Gatithini, and Ikumbo were identified as Lemna minor. In contrast, samples collected from Marimanti, Kathwana, and Kaanwa were identified as Lemna turionifera, Lemna aequinoctialis, and Lemma perpusilla, respectively. Lemna minor and Lemna turionifera were predominant in treated sewage ponds, while Lemna aequinoctialis and Lemma perpusilla were found on still waters in swamps and fishponds, respectively. This study provides baseline information that can be used in formulating conservation and utilization policies for duckweed in Tharaka-Nithi County and beyond.