Although the PLUTHERO name is very uncommon, there are two distinct branches. One north of the River Thames, centered around Kensington & Chiswich, the other south of the Thames at Richmond and came from Oxfordshire.
Todate the earliest listing is 1690 (Rousham Oxon) confirmed with speculative names dating back to 1505.
It is my contention that the branch split with two sons born to James (1742) giving birth to James (1762) and John (1764). It is here where James stayed in Middlesex and John into Surrey.
As far as I can see the origin of the name, is not what most people have speculated as being from Wales. I have been advised by an expert studying Welsh names that PLU could never be a Welsh name.
Where does it come from?
In Celtic, on the Brittany side, the word PLU means "village or parish" TH is a pronoun meaning "of or the" and ERO is "a small sandy strip between two points".
I firmly believe that about 1640 either a Hugonot added to their name (there are many Hugonot names with either PLU/PLUE/PLEW) the village that they originated from. It could have been PLU of THERER or something similar.
Another theory is that during those times, Brittany was famous for onions. Many natives of Brittany came to the UK to sell from door to door strings of onions from Brittany. One of those onion sellers could have taken residency in Middlesex and converted their name PLU to an English version.