Re-evaluating the species limits of Aponogeton kannangarae and Aponogeton jacobsenii using ISSR data

The genus Aponogeton comprises six species in Sri Lanka. Among those species, the recently described A. kannangarae closely resembles A. jacobsenii, in leaf morphology, especially colour, shape, and size. Even though differences in leaf base and follicle coat are recognized, a recent study questions the contribution of these morphological characters for recognizing it as a new species. This raises an ambiguity in the identification of A. jacobsenii and A. kannangarae as two different taxa. Since morphological data do not provide much strength to resolve ambiguities, a molecular study was conducted to gain additional evidence. The genetic distance of these two species was determined using ISSR (Inter Simple Sequence Repeats) - PCR amplification. Apart from these two species, another two morphologically similar species, A. rigidifolius and A. dassanayakei were used to obtain a clear idea about the species limits. The polymorphic bands that resulted from the ISSR- PCR amplification was coded into a data set and analyzed using the statistical software, PAST (Version 2.15). According to the cluster analysis, A. rigidifolius and A. dassanayakei are the two genetically closest species while A. jacobsenii has separated from A. rigidifolius, A. dassanayakei and A. kannangarae at a very early stage. Therefore, according to these studies, even though morphologically A. kannangarae and A. jacobsenii look similar, genetically, they are distantly related. Therefore, this molecular analysis strongly supports that A. kannangarae and A. jacobsenii are two different species.