The form which first comes, and is described and named, determines the specific character, and this long sticks as the type, though in fact it may be far from the most common form.

Yet of plants very well known in all their aspects, I can think of several of which we recognise two leading forms, and rarely see anything really intermediate, such as our Mentha borealis, its hairy and its smooth varieties.
Your former query about the variability of naturalised plants as compared with others of same genera, I had not forgotten, but have taken no steps to answer.

I was going hereafter to take up our list of naturalised plants and consider them--it did not fall into my plan to do it yet.

Off-hand I can only say that it does not strike me that our introduced plants generally are more variable, nor as variable, perhaps, as the indigenous.

But this is a mere guess.