The chromosome number for the Terschelling population of Ophioglossum vulgatum L., the only Netherland species of the genus, has been worked out. The original gametic number seems to be 240. Clones with higher numbers also exist in the area, as c. 248 bivalents have been found in a spore mother-cell of another spike of the same sample. On the basis of spore structure, the morphological variants are held to belong to the same species. Comparison with the earlier records is made, and a suggestion as to the origin of the various cytotypic clones is advanced. The writer’s earlier contention of a “gradual increase in the chromosome number from Northern to Southern latitudes in widely distributed species” (Verma 1958) seems to be well supported by the present sample.