Discrimination of the Species and Toxic Heavy Metal Contents of Alternanthera Sessilis (Sessile Joyweed), A. Philoxeroides (Alligator Weed) and Other Related Alternanthera Species

Abstract

Alternanthera sessilis [sessile joyweed (SJ)] is a staple leafy vegetable in Sri Lanka. However, A. philoxeroides [alligator weed (AW)] often gets mixed up with SJ due to the similar appearance. Alligator weed is an invasive species and also bio-accumulate toxic heavy metals. Genus Alternanthera has some other species that are occasionally being consumed in rural areas as leafy vegetables or grown as ornamental plants. It is essential to delimit AW from SJ and the rest of the Alternanthera species and study the heavy metal profiles of the shoot-top samples. In the present study, the species delimits and the phylogenetic relationships of the commonly grown A. philoxeroides, A. sessilis, A. caracasana, A. paronychioides, A. ficoidea, and A. bettzickiana were assessed using rbcL, ITS and matK-trnT DNA barcoding markers. The composition of the heavy metals in the market samples of the AW and SJ and field-grown samples of the other species were assessed using X-ray fluorescence (XRF) and Atomic Emission Spectroscopy (AES) methods. A. philixeroides and A. sessilis are positioned as sister taxa showing the close evolutionary relationship. The results showed that AW contains the highest amounts of the heavy metals, Pb and Sn. Red-SJ, a type of A. sessilis, contains the highest amount of As. The market samples of LS-1 and LS-2 did not contain significant levels of toxic heavy metals. The haplotypes of the markers ITS, and matK-trnT provide a clear basis to discriminate AW from the other Alternanthera spp.