Key to genera:
Tall climber - Leaves alternate: Piper
Small succulent herbs - Leaves opposite or whorled: Pepperomia.
https://books.google.co.uk/boo...
This is flora of the Sydney region, if the key relates to all Piperaceae then the drawings of Piper nigrum are wrong, Tropicas shows them as alternate.
http://www.tropicos.org/Name/2...
Piper with whorls of three, Piper polystachyon has three-nerved leaves. Note that the 's' is the historic 'f' shape.
https://books.google.co.uk/boo...
https://books.google.co.uk/boo...
