[But it also says that "Up to the turn of the 19th century, banjos were plucked and strummed by the fingers," and pictures from that time confirm that to have been the case.]

The 19th C. banjo styles were two in number (roughly speaking), both played with fingers ("guitar style") or the fingernail (down-picking, aka rapping, clawhammer, knocking, etc.) -- sometimes with a thimble (basically a fingerpick turned backwards).

The use of a plectrum (flat-pick) didn't come about till around 1910 or so. One instruction book from 1912 (I think) suggested removing the 5th string from a standard banjo and using a plectrum on the remaining strings (thereby inventing the plectrum banjo, the little-known 4-string melody instrument used in conjunction with the chord-oriented tenor banjo, which was invented a few years later).

The use of the tenor banjo in Irish music came about in the 1960s or so; Tommy Makem of the Clancy-Bros.-and- played a 5-string, but session musicians took up the tenor, playing melody instead of chords (which is what the tenor was used for in jass bands back in the day) sometime around that same time.

That's about all I know about it, I'm afraid.

Bob