The Virtanen type Finnish surnames are the surnames that became popular in the 19th century in western Finland and that are formed by combining of a word related to nature (but not an animal) with the suffix -nen.
[1][2] Until 2009 Virtanen was the most common surname in Finland, later superseded by Korhonen,[3][4] which is of unknown origin).
The suffix -nen, commonly used as a diminutive, was already in use in Eastern Finland (Savonia, Karelia) since the Middle Ages to create surnames in church records from the name of the parent (i.e., used as patronymic, e.g., Pentikäinen).
Most people in Western Finland lacked surnames, and in the era of Finnish national awakening Finns started adopting "Virtanen-type" surnames, which followed the pattern of the existing surnames in Eastern Finland, but without any personal association, and the suffix -nen acquired a new meaning of an abstract surname-generating suffix.
Later, the suffix -nen was often dropped altogether, and pairs of surnames, such as Lahtinen and Lahti, coexist.