Emex Necker ex Campd.
Emex is a genus of two closely related species, one native in the Mediterranean area and one native in South Africa (but both largely naturalised elsewhere). Both have been recorded as aliens in Belgium.
The two species of Emex are much alike but, at least originally, geographically distinct. When found together they readily hybridize, for instance in Australia (Putievsky & al. 1980).
Emex is much reminiscent of Spinacia oleracea and Tetragonia tetragonioides and might have been overlooked. Old Belgian collections of Emex were all erroneously identified as these species.
According to Sanchez & Kron (2008) Emex might better be included in Rumex and this was recently confirmed by more recent molecular studies (Schuster & al. 2015).
- Inner tepals of fruiting perianth broadly ovate, mucronate at apex. Spines of fruiting perianth ca. 4 mm long === 1. Emex australis
- Inner tepals of fruiting perianth lanceolate, acute at apex but not mucronate. Spines of fruiting perianth ca. 2 mm long === 2. E. spinosa
Literature:
Freeman C.C. (2005) Emex. In: Flora of North America Editorial Committee (eds.), Flora of North America, vol. 5. Oxford University Press, New York-Oxford: 487-488.
Galasso G., Banfi E., De Mattia F., Grassi F., Sgorbati S. & Labra M. (2009) Molecular phylogeny of Polygonum L. s.l. (Polygonoideae, Polygonaceae), focusing on European taxa: preliminary results and systematic considerations based on rbcL plastidial sequence data. Atti Soc. It. Sci. Nat. Museo Civ. Stor. Nat. Milano 150(1): 113-148.
Lousley J.E. & Kent D.H. (1981) Docks and knotweeds of the British Isles (BSBI Handbook n° 3). BSBI, London: 205 p.
Putievsky E., Weiss P.W. & Marshall D.R. (1980) Interspecific hybridization between Emex australis and E. spinosa. Austr. J. Bot. 28: 323-328.
Sanchez A. & Kron K.A. (2008) Phylogenetics of Polygonaceae with an emphasis on the evolution of Eriogonoideae. Syst. Bot. 33(1): 87-96.
Schuster T.M., Reveal J., Bayly M. & Kron K.A. (2015) An updated molecular phylogeny of Polygonoideae (Polygonaceae): Relationships of Oxygonum, Pteroxygonum, and Rumex, and a new circumscription of Koenigia. Taxon 64(6): 1188-1208. [available online at: https://www.researchgate.net/publication/288889005_An_updated_molecular_...