Hybridization in Dutch populations of Potentilla anglica, P. erecta and P. reptans was investigated. Chromosome counts were carried out for 342 plants collected from 40 populations. The chromosome number 2n = 56 was established for 52 plants all belonging to P. anglica, while 225 plants were found to possess 2n = 28. Of these 117 were identified as P. erecta and 108 as P. reptans. The number of 2n = 42 was counted for 50 specimens which belonged all, except 6 P. x mixta plants, to p. x suberecta. In 15 counts intermediate chromosome numbers were ascertained between 2n = 28 and 2n = 42, and between 2n = 42 and 2n = 56, which most probably were due to back crossing of P. x suberecta with one of the parental species. P. x suberecta was found in 13 populations and P. x mixta in only two. The hybrid P. erecta x reptans was not met with. Detailed study of some P. x suberecta populations revealed that this hybrid always grew mixed up with P. erecta, often in large quantities. In morphological characters and ecological amplitude it ranged from P. erecta to P. anglica. Its pollen and fruit fertility was c. 1/3 respectively c. 2/3 of that of the parental species. The functioning of the pollen was investigated in five P. erecta populations. Transport of pollen was found to occur by wind, but chiefly by insects from the families; Syrphidae, Muscidae, Tachninidae, Chloropidae and Thripidae. Artificial cross fertilisation yielded more mature seeds than id. self fertilisation, while apogamy was not demonstrated. Finally, literature data and own observations were combined in a hybridization scheme.