Research workers in Latvia have revealed (2009) high levels of ascorbic acid and other beneficial compounds in the fruits of many cultivars and hybrids of the rowan (Sorbus aucuparia).
The authors point out that the first sweet rowan berry clones were selected in the Sudety mountain area in what is now the Czech Republic. In Russia the celebrated plant geneticist Ivan Vladimirovich Michurin started a breeding program for sweet rowan berries at the beginning of the 20th century and this resulted in hybrids of the rowan with aronia, apple, medlar and pear species.
The rowans studied in Latvia included the unimproved wild rowan, and the cultivars 'Rosina', 'Rosina Variegata', Zholtaya and Krasnaya Krupnaya as well as several of the hybrids.
The highest content of ascorbic acid (Vitamin C) was found in the two 'Rosina' cultivars, but all did well and were rich in a wide range of other beneficial compounds.
Full details are below (the text is in English as well as Latvian.)
Kampus, K. et al. (2009) Biochemical composition and antiradical activity of Rowanberry (Sorbus L.) and hybrids with different Rosaceae cultivars. Agronomijas Vestis (Latvian Journal of Agronomy) No. 12 (2009): 59-64. http://llufb.llu.lv/conference/agrvestis/content/n12/Latvia-Agronomijas-Vestis-12-2009.pdf