Phlox paniculata  

Phlox paniculata L. (USA) – A rare and usually ephemeral escape from or relic of cultivation, or a mere throw-out (sometimes more or less temporarily persisting). First documented from a railway siding in Mol in 2009 but probably long neglected before. Since then regularly recorded in several widely scattered localities. An up-to-date overview of Belgian records is available here: https://waarnemingen.be/soort/view/137460.
Phlox paniculata is usually seen in small numbers (often single clones) on rough ground, by roadsides and railway tracks, near gardens, etc. It is still frequently cultivated as an ornamental in gardens (it is the most popular species of the genus in gardens) although perhaps less so than in the past.
Phlox paniculata is a highly variable species and this certainly holds true for plants found in horticulture. More than 100 cultivars have been described (Brown 2000) and some ‘races’ offered by the horticultural trade probably represent hybrids between closely related species. The separation, for instance, of Phlox paniculata and P. maculata L. is rarely straightforward. Typical plants of the latter have been recorded as escapes in Belgium (prior to 1950). They tend to have stems that are more conspicuously streaked with purple, entire leaves with glabrous margins and less distinct lateral veins. Many of the plants seen nowadays in Belgium are more or less intermediate: leaves are often (sub-) entire with minutely ciliate margins, unstreaked stems, distinctly hairy corolla tubes, etc. Therefore, in horticulture (and as escapes) Phlox paniculata is probably better referred to as a complex of species, the Phlox paniculata group, as per Clement & Foster (1994).

Selected literature

Brown N. (2000) Phlox. In: Cullen J. & al. (eds.), The European Garden Flora, vol. 6. Cambridge University Press, Cambridge: 104-109.

Clement E.J. & Foster M.C. (1994) Alien plants of the British Isles. BSBI, London: XVIII + 590 p.