Phyla nodiflora (L.) E. Greene var. minor (Hook.) N. O’Leary et Múlgura (syn.: P. canescens (Kunth) E. Greene, P. nodiflora var. canescens (Kunth) Moldenke, P. filiformis (Schrad.) Meikle, Lippia filiformis Schrad., Lippia canescens Kunth) (Trop.) – A very rare escape from cultivation. Recorded twice so far in Belgium: in 2010 seen self-sown on pavement near a garden in Geel (see also: http://waarnemingen.be/waarneming/view/49555886#). In 2011 furthermore seen on a grassy talus slope in Essen (see also: http://waarnemingen.be/waarneming/view/55839846#), possibly as a garden throw-out. In the latter locality it looks firmly established.
The exact identity of plants in cultivation is somewhat uncertain. The distinction of Phyla canescens and P. nodiflora appears to be critical. Recent authors therefore include both taxa in one variable species (O’Leary & Múlgura 2012). In the plants seen so far in the wild in Belgium corollas are obviously not white and relatively large (pinkish-lilac and ca. 3 mm across), leaves are subentire to shallowly toothed with 2-3 teeth on either side and densely appressed strigose and the calyx is divided (much) less than half way to base. These features correspond with Phyla canescens but plants in cultivation might as well represent cultivars or hybrids. Genetic analyses by Gross & al. (2017) strongly supported the treatment of P. canescens of a separate species.
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Selected literature:
Gross C.L., Fatemi M., Julien M., McPherson H. & Van Klinken R. (2017) The Phylogeny and Biogeography of Phyla nodiflora (Verbenaceae) Reveals Native and Invasive Lineages throughout the World. Diversity 9, 20. [available online at: https://www.mdpi.com/1424-2818/9/2/20]
O’Leary N. & Múlgura M.E. (2012) A taxonomic revision of the genus Phyla (Verbenaceae). Ann. Missouri Bot. Gard. 98: 578-596.