A population ofOphioglossum reticulatumL. growing in an area of c. 1500 sq. metres in Darbhanga (N. Bihar), India exhibited marked morphological differences. Sampling of the morphological variants led to the delimitation of five groups in the population. Of this, three were confined to moist shady place and the other two to open dry condition. Meiotic investigations carried out in these groups revealed differences in chromosome numbers which indicated different ploidy levels. The lowest number of 112–114 bivalents and 8–12 univalents has been encountered in one group and constitutes the first report of a diploid count from this country. Other numbers counted were 194–200 bivalents, 375–380 bivalents and 632–640 bivalents with 6–12 univalents in each. The univalents may represent fragments. Polyploidy has been suggested to be the dominant genetic theme in homosporous pteriodophytes. Storage and release of genetic variability through polyploidy may have provided evolutionary adaptability to this genus, known for its ancient history and high number of chromosomes.