....
If I get it wrong when using my field guide to identify wild rocket
(actually, in my Collins FG, 'Hedge mustard' is what they call
Sisymbrium officinale, which in turn is what the Internet seems to
call 'wild rocket'), eating the wrong close relative won't do me any
harm, will it?

Just as a matter of interest, why is "wild rocket" in the supermarket called
"wild rocket" in the first place??