Rhubarbium

From Memory Alpha, the free Star Trek reference.

Name:	Rhubarbium
Symbol:	Rb
Atomic Number:	Unknown
Atomic Weight:	37

Rhubarbium is a chemical element listed on the Table of Elements. (TNG: "Rascals")

The element Rhubarbium had the symbol "Rb" which is the same atomic symbol used for Rubidium. It is presumably named after the vegetable Rhubarb.