Acanthus L.
Acanthus is a genus of ca. 22 species, native to the warm-temperate regions and the tropics of the Old World (especially tropical Africa). All European and some western Asian species are cultivated as ornamentals (Brummitt 2000, Jäger & al. 2008). The identity of at least some of the currently grown species is critical. Some represent complex hybrids involving Acanthus mollis, A. hungaricus (Borbás) Baenitz and A. spinosus L. (Brummitt l.c.).
Molecular phylogenetic studies confirmed its monophyly (McDade & Moody 1999).
Two more or less distinct entities can be separated in Belgium:
1 Leaf lobes acute but not spiny. Stem, leaves and bracts usually glabrous === A. mollis
Leaf lobes with spiny teeth. Stem, leaves and bracts often hairy, at least in part === A. spinosus
Literature:
Brummitt R.K. (2000) Acanthus. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge UniversityPress, Cambridge: 364-366.
Jäger E.J., Ebel F., Hanelt P. & Müller G. (eds.) (2008) Rothmaler Band 5.Exkursionsflora von Deutschland. KrautigeZier-und Nutzpflanzen. Springer Verlag, Berlin: 880 p.
McDade L.A. & Moody M.L. (1999) Phylogenetic relationships among Acanthaceae: evidence from noncoding trnL-trnF chloroplast DNA sequences. Am. J. Bot. 86(1): 70-80. [available online at: http://www.amjbot.org/content/86/1/70.full]
Rix M. (1980) The genus Acanthus L. An introduction to the hardy species.The Plantsman2: 132-140.
Vollesen K.(2007) Synopsis of the species of Acanthus (Acanthaceae) in tropical East and Northeast Africa and in tropical Arabia.Kew Bull.62(2): 233-249.