1. Åberg, E. (1940). Symb. bot. upsal., 4, 1–150.
2. Åberg, E. (1948). Ann. R. agric. Coll. Sweden, 15, 235–250.
3. Åberg, E. (1957). Ann. R. agric. Coll. Sweden, 23, 315–322.
4. Åberg, E. and Wiebe, G.A. (1945). J. Wash. Acad. Sci., 35, 161–164.
5. AI-Aish, M. and Brown, W.V. (1958). Am. J. Bot., 45, 16–23.