Verbena, as currently circumscribed (see for instance Sanders 2001), is a genus of ca. 50 species. It traditionally falls apart into two more or less distinct sections: section Verbena with most representatives in North America and section Pachystachyae Schauer with chiefly South American species. Non-native taxa of both sections occur in Belgium and one species, Verbena officinalis L., is native. Nesom (2010) recently proposed a slightly modified infrageneric classification.
Verbena hastata L. (syn.: V. paniculata Lam.) (N-Am.) – A rare and ephemeral alien, formerly associated with the wool-processing industry in the Vesdre valley (between 1902-1947). Recently increasingly recorded, mostly in the province of Limburg, for instance in 1995 along river Maas in Uikhoven. Discovered in 2008 in Zolder (railway track), Balen (former dump) and Lommel (ground heaps), usually single specimens but sometimes persisting for some time. Furthermore recorded in 2001 on a sand-raised site in the port of Gent. In 2009 also seen on a derelict maize field in Lauwe. Since then rather regularly seen, for instance in Eksel, Geel, Kortrijk, Mol, Overpelt, etc. The exact vector of introduction is not always obvious: some records probably represent garden escapes but others are hardly explainable.
The generic limits of some Verbenaceae and the familial circumscription have slightly changed in recent times. Glandularia, long included in Verbena, is nowadays accepted at the generic level (Sanders 2001, O’Leary & al. 2007, Mabberley 2008). Caryopteris and Clerodendrum, formerly thought to belong to Verbenaceae, are now accommodated in Lamiaceae (Cantino & al. 1992, Marx & al. 2010).