Viola hirta (Violaceae) and its relatives in Norway

Viola hirta is widespread in most of Europe but rare in Norway, occurring in four isolated enclaves around the Oslo Fjord. Allozymic and morphological patterns of variation were studied in 320 individuals of Viola hirta (2n = 20) and its relatives V. collina (2n = 20), V. odorata (2n = 20), and V. suavis (2n = 40) from 22 Norwegian populations. Ongoing introgression from both V. collina and V. odorata, as hypothesised by several authors, was not supported by our data. All hybrids proved to be primary ones and, apparently, introgression is rare. However, allozyme markers suggested that V. hirta may have been affected by ancient introgression from V collina and possibly also from the East European V. ambigua (2n = 40) during its evolutionary history. Geographical differentiation, presumably relatively recent and post-glacial, was evident in V. hirta. Variation occurred also between and within V. odorata populations, most likely a consequence of independent introductions by man. No variation was observed in V. collina or in V. suavis. A key to the Norwegian species of subsection Viola and their primary hybrids based on morphological characters is provided in Flora Nordica note No. 26.