The extent of genetic diversity within a species is an important determinant of successful adaptation to adverse environmental conditions. Assessment of extent of genetic diversity/variability is also important to monitor genetic erosion within a species. In threatened plant species, genetic diversity assessment helps in selection of genetically diverse populations to enrich the genetically impoverished populations, thus minimizing the probability of genetic drift. Confirming taxonomic identity of threatened species, particularly those belonging to species complexes with dispute identity, is another essential task in the conservation of threatened species, which is best resolved through molecular approaches. The present study estimated the genetic variability within and among the populations of four threatened species, viz. Justicia beddomei (C.B. Clarke) Bennet (Acanthaceae), Embelia ribes Burm. f. (Myrsinaceae), Madhuca insignis (Radlk.) H.J. Lam (Sapotaceae) and Cycas beddomei Dyer (Cycadaceae) using Inter Simple Sequence Repeat (ISSR) and Simple Sequence Repeat (SSR) markers for selecting the genetically diverse populations. The phylogeny was analysed through ITS (nrDNA) and matK (cpDNA) sequences to confirm the species identity.
The phylogenetic analyses confirmed four distinct species of Justicia, which also revealed that J. beddomei and J. adhatoda were sister groups with a common ancestor showing rapid parallel speciation with J. gendarussa in one clade and J. betonica in another. Madhuca insignis with extremely small population in the Western Ghats (Karnataka to Kerala) might have undergone either extensive hybridization or incipient speciation. In case of Embelia species, a greater evolutionary closeness between E. subcoraceae and E. floribunda was revealed, while E. ribes had a distinct clad. Both ISSR and SSR markers distinguished various genotypes of Cycas beddomei.