I had a taster of this watching Emma on Netflix with my daughter a couple of days ago. Suddenly I sat up straight, exclaiming, "But that's a well-established wisteria! And Emma was published in 1815!"
As you will know, wisteria was not introduced to Britain until the following year, and took several years to flower. (I would not know this but that wisteria is a flower that I've taken a particular interest in, because Japan.)
"You're just like X!" she said, naming her boyfriend. "When we watched North and South he couldn't get beyond the naturalised sycamores."
Now I wonder whether the country is full of frustrated horticulturalists who daren't watch anything set before 1860, for fear of spotting an exotic.