Sulla is a segregate of Hedysarum L. and corresponds with the latter’s section Spinosissima (Choi & al. 1999, Choi & Ohashi 2003). Its generic status has been questioned (e.g. Ahangarian & al. 2007). Recent molecular data, however, showed it to be monophyletic and well separated from Hedysarum s.str. (e.g. Amirahmadi & al. 2014, Duan & al. 2015). Apart from Alhagi, Sulla forms a well-supported clade sister to the rest of the Hedysaroid clade. The genus is indigenous from Siberia, central-western Asia to the European Mediterranean region and North Africa and counts eight species (Amirahmadi & al. 2014). One out of these, Sulla coronaria, is sometimes cultivated for fodder (Italian sainfoin) and often occurs as an escape outside its native distribution area. It has been found as an alien in Belgium.
Ahangarian S., Kazempour Osaloo Sh. & Maassoumi A.A. (2007) Molecular phylogeny of the tribe Hedysareae with special reference to Onobrychis (Fabaceae) as inferred from nrDNA ITS sequences. Iran. J. Bot. 13(2): 64-74. [available online at: http://www.sid.ir/en/vewssid/j_pdf/105320072601.pdf]
Amirahmadi A., Osaloo S.K., Moein F., Kaveh A. & Maassoumi A.A. (2014) Molecular systematics of the tribe Hedysareae (Fabaceae) based on nrDNA ITS and plastid trnL-F and matK sequences. Pl. Syst. Evol. 300: 729-747.
Choi B.H., Nemoto T. & Ohashi H. (1999) Anatomy of nodal regions and leaves in Hedysarum and related genera (Leguminosae). J. Jap. Bot. 74: 236-250.
Choi B.H. & Ohashi H. (2003) Generic criteria and an infrageneric system for Hedysarum and related genera (Papilionoideae-Leguminosae). Taxon 52: 567-576.
Duan L., Wen J., Yang X., Liu P.-L., Arslan E., Ertuğrul K. & Chang Z.-Y. (2015) Phylogeny of Hedysarum and tribe Hedysareae (Leguminosae: Papilionoideae) inferred from sequence data of ITS, matK, trnL-F and psbA-trnH. Taxon 64(1): 49-64. [available online at: https://www.researchgate.net/publication/273160030_Phylogeny_of_Hedysaru...
Fedtschenko B.A. (1902) The genus Hedysarum (in Russian). Acta Horti Petrop. 19: 185-375. [available online at: http://www.biodiversitylibrary.org/item/53230#page/2/mode/1up]