Verbena bonariensis
Verbena bonariensis L. (S-Am.) – Formerly regularly recorded as an ephemeral wool alien in the Vesdre valley, at least between 1893 and 1959. Nowadays much cultivated as an ornamental and frequently escaping, especially in urban areas. Most often seen on pavement or old walls. Also frequently seen on dumps. Identical records are available for several other western European countries (Clement 2002, van der Meijden & Holverda 2006,…). Verbena bonariensis is usually rather ephemeral but locally persists very well. Several plants are known for instance from a quay in the port of Oostende since at least 2000.
The Belgian populations of Verbena bonariensis are rather heterogeneous. Two more or less distinct varieties have been observed: var. bonariensis and var. conglomerata Briq. They are distinguished in the following couplet:
- Spikes cylindrical, not contracted in capitate clusters. Corollas small, hardly exceeding calyx. Inflorescence usually eglandular === var. bonariensis
- Spikes contracted into capitate clusters. Corolla larger, at least twice as long as calyx. Inflorescence glandular === var. conglomerata
Variety bonariensis is a weedy taxon without ornamental value and formerly occurred in the Vesdre valley as a wool alien. All present-day records belong to var. conglomerata, a taxon with showier corollas and much more appropriate for horticultural purposes.
Verbena incompta is an enigmatic taxon, more or less intermediate and much confused with Verbena brasiliensis and V. bonariensis (Yeo 1989, Michael 1995). Recent taxonomists merely placed it in the synonymy of Verbena bonariensis (Munir 2002, O’Leary & al. 2007) but Nesom (2010), in his preparation of a taxonomic treatment for the developing Flora of North America, unequivocally accepts Verbena incompta as a species of its own. It is naturalized in parts of southwestern Europe (Italy, Spain) and was recently recorded for the first time in Belgium as well (see there).
According to Clement (2002) the plant currently found in gardens might be a recently stabilised hybrid that now breeds true. Nesom (2010) does not distinguish between cultivated (var. conglomerata?) and wild races of Verbena bonariensis.
Selected literature
Clement E.J. (2002) Some notes on Verbena bonariensis L. sensu lato. BSBI News 89: 37-43.
Lawalrée A. (1953) Contribution à l’étude de la flore adventice de la Belgique. Bull. Soc. Roy. Bot. Belg. 86: 137-143.
Michael P.W. (1995) A new name for a widespread and misunderstood species of Verbena (Verbenaceae). Telopea 6: 181-183.
Munir A.A. (2002) A taxonomic revision of the genus Verbena L. (Verbenaceae) in Australia. J. Adelaide Bot. Gard. 20: 21-103.
Nesom G.L. (2010) Taxonomic notes on Verbena bonariensis (Verbenaceae) and related species in the USA. Phytoneuron 2010-12: 1-16.
O’Leary N., Múlgura M.E. & Morrone O. (2007) Revisión taxonómica de las especies del género Verbena (Verbenaceae): serie Pachystachyae. Ann. Missouri Bot. Gard. 94: 571-622.
Van der Meijden R. & Holverda W. (2006) Nieuwe vondsten van zeldzame planten in 2003 en 2004. Gorteria 32: 1-33.
Yeo P.F. (1989) A re-definition of Verbena brasiliensis. Kew Bull. 45: 101-120.