Ophioglossum L. commonly known as "adder's tongue fern", has been of great interest due to the highest number of chromosomes in any organism so far known in biological world. Here, a new species of adder's tongue fern has been discovered and reported from Western Ghats of India. It is prominently distinct from the other known taxa in Ophioglossaceae family. Phylogenetic analysis of three chloroplast DNA (cpDNA) regions (trnL-F, rbcL and psbA-trnH) unambiguously designate this adder's tongue fern as the distinct lineage and is sister to the clade containing O. parvifolium and O. nudicaule. Azolla caroliniana - an aquatic fern (average size, 0.5-1.5 cm), is the smallest fern on the earth. Our discovery discloses a new species of adder's tongue fern and ranking it among the smallest terrestrial fern in the world, attaining an average size of only 1-1.2 cm.