Symphyotrichum xversicolor (Willd.) Nesom (= S. laeve (L.) Á. et D. Löve var. laeve x S. novi-belgii var. novi-belgii; syn.: Aster xversicolor Willd.) (hort.) – A rather frequently naturalized escape from cultivation. With S. lanceolatum doubtlessly the most widespread taxon in Belgium. It is found in a wide range of usually human-mediated habitats (it is particularly common by railway tracks).
This species is usually easily distinguished from its putative parents. Its phyllaries are distinctly unequal and tightly appressed (subequal and loose in Symphyotrichum novi-belgii). S. laeve, the other parent species, is distinctly glaucous and somewhat smaller but otherwise very similar to S. xversicolor. Compared with S. lanceolatum the phyllaries of S. xversicolor are wider (more than 0.7 mm) and with a wider green median part.
At present, Symphyotrichum laeve is probably mostly replaced by S. xversicolor in Europe, in horticulture as well as in the wild. However, a single population from Brakel, discovered in 2013, seems to match rather well genuine S. laeve (see photos).
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